diff --git a/melib/src/lib.rs b/melib/src/lib.rs
index 80e80ae5..c50086d2 100644
--- a/melib/src/lib.rs
+++ b/melib/src/lib.rs
@@ -110,6 +110,7 @@ pub use addressbook::*;
 pub mod backends;
 pub use backends::*;
 mod collection;
+pub mod sieve;
 pub use collection::*;
 pub mod conf;
 pub use conf::*;
diff --git a/melib/src/parsec.rs b/melib/src/parsec.rs
index 8eebf608..c4205b19 100644
--- a/melib/src/parsec.rs
+++ b/melib/src/parsec.rs
@@ -267,6 +267,76 @@ where
     }
 }
 
+pub fn pairmutation<'a, P1, P2, R1, R2>(parser1: P1, parser2: P2) -> impl Parser<'a, (R1, R2)>
+where
+    P1: Parser<'a, R1>,
+    P2: Parser<'a, R2>,
+{
+    move |input| {
+        if let ok @ Ok(_) = parser1.parse(input).and_then(|(next_input, result1)| {
+            parser2
+                .parse(next_input)
+                .map(|(last_input, result2)| (last_input, (result1, result2)))
+        }) {
+            return ok;
+        }
+        parser2.parse(input).and_then(|(next_input, result1)| {
+            parser1
+                .parse(next_input)
+                .map(|(last_input, result2)| (last_input, (result2, result1)))
+        })
+    }
+}
+
+#[macro_export]
+macro_rules! permutation {
+    ($input:expr, $($field:tt, $t:ty, $parser:expr),*) => {{
+        'perm: {
+            struct PermStruct {
+                $($field: Option<$t>),*
+            }
+            let mut results = PermStruct {
+                $($field: None),*
+            };
+            let mut input = $input;
+            let mut left = 0;
+            $(_ = &$parser; left += 1;)*
+            let mut count = 1;
+            let mut finished = 0;
+            loop {
+                let mut any_success = false;
+                $(if results.$field.is_none() {
+                    if let Ok((rest, res)) = $parser.parse(input) {
+                        if !matches!(res, None) || count > left {
+                            results.$field = Some(res);
+                            finished += 1;
+                            count = 1;
+                            input = rest;
+                        }
+                        any_success = true;
+                    }
+                })*
+                count += 1;
+
+                if !any_success {
+                    break 'perm Err(input);
+                }
+                if finished == left || count >= 2*left {
+                    break;
+                }
+
+            }
+            if finished != left {
+                break 'perm Err(input);
+            }
+            let PermStruct {
+                $($field),*
+            } = results;
+            Ok((input, ($($field.unwrap()),*)))
+        }
+    }}
+}
+
 pub fn prefix<'a, PN, P, R, RN>(pre: PN, parser: P) -> impl Parser<'a, R>
 where
     PN: Parser<'a, RN>,
@@ -293,9 +363,14 @@ where
     }
 }
 
-pub fn delimited<'a, PN, RN, P, R>(lparser: PN, mid: P, rparser: PN) -> impl Parser<'a, R>
+pub fn delimited<'a, PNL, PNR, LN, RN, P, R>(
+    lparser: PNL,
+    mid: P,
+    rparser: PNR,
+) -> impl Parser<'a, R>
 where
-    PN: Parser<'a, RN>,
+    PNL: Parser<'a, LN>,
+    PNR: Parser<'a, RN>,
     P: Parser<'a, R>,
 {
     move |input| {
diff --git a/melib/src/sieve.rs b/melib/src/sieve.rs
new file mode 100644
index 00000000..60da6432
--- /dev/null
+++ b/melib/src/sieve.rs
@@ -0,0 +1,1018 @@
+/*
+ * melib - sieve module
+ *
+ * Copyright 2022 Manos Pitsidianakis
+ *
+ * This file is part of meli.
+ *
+ * meli is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * meli is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with meli. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+use crate::parsec::*;
+
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct RuleBlock(pub Vec<Rule>);
+
+/*
+   MATCH-TYPE =/ COUNT / VALUE
+
+  COUNT = ":count" relational-match
+
+  VALUE = ":value" relational-match
+
+  relational-match = DQUOTE
+          ("gt" / "ge" / "lt" / "le" / "eq" / "ne") DQUOTE
+          ; "gt" means "greater than", the C operator ">".
+          ; "ge" means "greater than or equal", the C operator ">=".
+          ; "lt" means "less than", the C operator "<".
+          ; "le" means "less than or equal", the C operator "<=".
+          ; "eq" means "equal to", the C operator "==".
+          ; "ne" means "not equal to", the C operator "!=".
+*/
+#[derive(Debug, PartialEq, Eq, Clone)]
+pub enum ActionCommand {
+    Keep,
+    Fileinto { mailbox: String },
+    Redirect { address: String },
+    Discard,
+}
+
+#[derive(Debug, PartialEq, Eq, Clone)]
+pub enum ControlCommand {
+    Stop,
+    Require(Vec<String>),
+    If {
+        condition: (ConditionRule, RuleBlock),
+        elsif: Option<(ConditionRule, RuleBlock)>,
+        else_: Option<RuleBlock>,
+    },
+}
+
+#[derive(Debug, PartialEq, Eq, Clone)]
+pub enum Rule {
+    Block(RuleBlock),
+    Action(ActionCommand),
+    Control(ControlCommand),
+}
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum AddressOperator {
+    All,
+    Localpart,
+    Domain,
+}
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum IntegerOperator {
+    Over,
+    Under,
+}
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+/// RFC 5231 Sieve Email Filtering: Relational Extension
+pub enum RelationalMatch {
+    /// "gt" means "greater than", the C operator ">".
+    Gt,
+    /// "ge" means "greater than or equal", the C operator ">=".
+    Ge,
+    /// "lt" means "less than", the C operator "<".
+    Lt,
+    /// "le" means "less than or equal", the C operator "<=".
+    Le,
+    /// "eq" means "equal to", the C operator "==".
+    Eq,
+    /// "ne" means "not equal to", the C operator "!=".
+    Ne,
+}
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum MatchOperator {
+    Is,
+    Matches,
+    Contains,
+    Count(RelationalMatch),
+    Value(RelationalMatch),
+}
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum CharacterOperator {
+    /// i;octet,
+    Octet,
+    ///i;ascii-casemap
+    AsciiCasemap,
+}
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum ZoneRule {
+    /// "year"      => the year, "0000" .. "9999".
+    Year,
+    /// "month"     => the month, "01" .. "12".
+    Month,
+    /// "day"       => the day, "01" .. "31".
+    Day,
+    /// "date"      => the date in "yyyy-mm-dd" format.
+    Date,
+    /// "julian"    => the Modified Julian Day, that is, the date
+    /// expressed as an integer number of days since
+    /// 00:00 UTC on November 17, 1858 (using the Gregorian
+    /// calendar).  This corresponds to the regular
+    /// Julian Day minus 2400000.5.  Sample routines to
+    /// convert to and from modified Julian dates are
+    /// given in Appendix A.
+    Julian,
+    /// "hour"      => the hour, "00" .. "23".
+    Hour,
+    /// "minute"    => the minute, "00" .. "59".
+    Minute,
+    /// "second"    => the second, "00" .. "60".
+    Second,
+    /// "time"      => the time in "hh:mm:ss" format.
+    Time,
+    /// "iso8601"   => the date and time in restricted ISO 8601 format.
+    Iso8601,
+    /// "std11"     => the date and time in a format appropriate
+    /// for use in a Date: header field [RFC2822].
+    Std11,
+    /// "zone"      => the time zone in use.  If the user specified a
+    ///time zone with ":zone", "zone" will
+    ///contain that value.  If :originalzone is specified
+    ///this value will be the original zone specified
+    ///in the date-time value.  If neither argument is
+    ///specified the value will be the server's default
+    ///time zone in offset format "+hhmm" or "-hhmm".  An
+    ///offset of 0 (Zulu) always has a positive sign.
+    Zone,
+    /// "weekday"   => the day of the week expressed as an integer between "0" and "6". "0" is Sunday, "1" is Monday, etc.
+    Weekday,
+}
+
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub enum ConditionRule {
+    /// Logical OR operation.
+    AnyOf(Vec<ConditionRule>),
+    /// Logical AND operation.
+    AllOf(Vec<ConditionRule>),
+    /// Header values exist.
+    Exists(Vec<String>),
+    Header {
+        comparator: Option<CharacterOperator>,
+        match_operator: Option<MatchOperator>,
+        header_names: Vec<String>,
+        key_list: Vec<String>,
+    },
+    Date {
+        comparator: Option<CharacterOperator>,
+        match_type: Option<MatchOperator>,
+        zone: ZoneRule,
+        header_name: String,
+        date_part: String,
+        key_list: Vec<String>,
+    },
+    Address {
+        comparator: Option<CharacterOperator>,
+        address_part: Option<AddressOperator>,
+        match_type: Option<MatchOperator>,
+        header_list: Vec<String>,
+        key_list: Vec<String>,
+    },
+    Not(Box<ConditionRule>),
+    Size {
+        operator: IntegerOperator,
+        limit: u64,
+    },
+    Literal(bool),
+}
+
+pub mod parser {
+    use super::*;
+    macro_rules! parse_action {
+        ($parser_name:ident, $lit:literal, $t:ty, $action:expr) => {
+            pub fn $parser_name<'a>() -> impl Parser<'a, $t> {
+                move |input| {
+                    map(
+                        ws(right(match_literal_anycase($lit), ws(match_literal(";")))),
+                        |_| $action,
+                    )
+                    .parse(input)
+                }
+            }
+        };
+        ($parser_name:ident, $lit:literal, $t:ty, $action:expr, $argument:ident) => {
+            pub fn $parser_name<'a>() -> impl Parser<'a, $t> {
+                move |input| {
+                    map(
+                        ws(right(
+                            parse_token($lit),
+                            left(ws(string()), ws(parse_token(";"))),
+                        )),
+                        |$argument| $action,
+                    )
+                    .parse(input)
+                }
+            }
+        };
+    }
+
+    parse_action! { parse_sieve_keep, "keep", ActionCommand, ActionCommand::Keep }
+    parse_action! { parse_sieve_discard, "discard", ActionCommand, ActionCommand::Discard }
+    parse_action! { parse_sieve_stop, "stop", ControlCommand, ControlCommand::Stop }
+    parse_action! { parse_sieve_fileinto, "fileinto", ActionCommand, ActionCommand::Fileinto { mailbox }, mailbox }
+    parse_action! { parse_sieve_redirect, "redirect", ActionCommand, ActionCommand::Redirect { address }, address }
+
+    #[inline(always)]
+    pub fn parse_token<'a>(literal: &'static str) -> impl Parser<'a, ()> {
+        move |input| map(ws(match_literal_anycase(literal)), |_| ()).parse(input)
+    }
+
+    #[inline(always)]
+    fn ws_inner<'a>() -> impl Parser<'a, ()> {
+        move |input: &'a str| {
+            let mut offset = 0;
+            let input_b = input.as_bytes();
+            while offset < input_b.len() {
+                while offset < input_b.len()
+                    && [b' ', b'\t', b'\n', b'\r'].contains(&input_b[offset])
+                {
+                    offset += 1;
+                }
+                if offset >= input_b.len() {
+                    break;
+                }
+                if input_b[offset] == b'#' {
+                    while offset < input_b.len()
+                        && !input[offset..].starts_with("\r\n")
+                        && !input[offset..].starts_with('\n')
+                    {
+                        offset += 1;
+                    }
+                    if offset >= input_b.len() {
+                        break;
+                    }
+                    if input[offset..].starts_with("\r\n") {
+                        offset += 2;
+                    } else if input[offset..].starts_with('\n') {
+                        offset += 1;
+                    }
+                } else if input[offset..].starts_with("/*") {
+                    while offset < input_b.len() && !input[offset..].starts_with("*/") {
+                        offset += 1;
+                    }
+                    if offset >= input_b.len() {
+                        break;
+                    }
+                    if input[offset..].starts_with("*/") {
+                        offset += 2;
+                    }
+                } else {
+                    break;
+                }
+            }
+            Ok((&input[offset..], ()))
+        }
+    }
+
+    pub fn ws<'a, P, A>(parser: P) -> impl Parser<'a, A>
+    where
+        P: Parser<'a, A>,
+    {
+        move |input1| {
+            let (input2, ()) = ws_inner().parse(input1)?;
+            let (input3, res) = parser.parse(input2)?;
+            let (input4, ()) = ws_inner().parse(input3)?;
+            Ok((input4, res))
+        }
+    }
+
+    // string       = quoted-string / multi-line
+    //
+    // quoted-other       = "\" octet-not-qspecial
+    //                        ; represents just the octet-no-qspecial
+    //                        ; character.  SHOULD NOT be used
+
+    // quoted-safe        = CRLF / octet-not-qspecial
+    //                        ; either a CRLF pair, OR a single octet other
+    //                        ; than NUL, CR, LF, double-quote, or backslash
+
+    // quoted-special     = "\" (DQUOTE / "\")
+    //                        ; represents just a double-quote or backslash
+
+    // quoted-string      = DQUOTE quoted-text DQUOTE
+
+    // quoted-text        = *(quoted-safe / quoted-special / quoted-other)
+
+    pub fn string<'a>() -> impl Parser<'a, String> {
+        #[inline(always)]
+        fn quoted_text<'a>() -> impl Parser<'a, String> {
+            move |input: &'a str| {
+                let mut offset = 0;
+                let mut unescape_dquote: bool = false;
+                let mut unescape_slash: bool = false;
+                while offset < input.len() {
+                    if input.len() >= offset + 2 {
+                        if input.starts_with("\r\n") {
+                            offset += 2;
+                        } else if input.starts_with("\\\"") {
+                            unescape_dquote = true;
+                            offset += 2;
+                        } else if input.starts_with("\\\\") {
+                            unescape_slash = true;
+                            offset += 2;
+                        }
+                    }
+                    // a single octet other ; than NUL, CR, LF, double-quote, or backslash
+                    if [b'\x00', b'\r', b'\n', b'"', b'\\'].contains(&input.as_bytes()[offset]) {
+                        break;
+                    }
+                    offset += 1;
+                }
+                match (unescape_dquote, unescape_slash) {
+                    (false, false) => Ok((&input[offset..], input[..offset].to_string())),
+                    (true, false) => Ok((&input[offset..], input[..offset].replace("\\\"", "\""))),
+                    (false, true) => Ok((&input[offset..], input[..offset].replace("\\\\", "\\"))),
+                    (true, true) => Ok((
+                        &input[offset..],
+                        input[..offset].replace("\\\"", "\"").replace("\\\\", "\\"),
+                    )),
+                }
+            }
+        }
+
+        #[inline(always)]
+        fn quoted_string<'a>() -> impl Parser<'a, String> {
+            delimited(parse_token("\""), quoted_text(), parse_token("\""))
+        }
+
+        //fn multiline() -> impl Parser<'a, String> {}
+        //either(quoted_string(), multiline())
+        quoted_string()
+    }
+
+    #[inline(always)]
+    pub fn literal_map<'a, T: Clone>(literal: &'static str, value: T) -> impl Parser<'a, T> {
+        move |input| map(parse_token(literal), |_| value.clone()).parse(input)
+    }
+
+    // number             = 1*DIGIT [ QUANTIFIER ]
+    // QUANTIFIER         = "K" / "M" / "G"
+    pub fn number<'a>() -> impl Parser<'a, u64> {
+        map_res(
+            pair(
+                is_a(b"0123456789"),
+                pred(any_char, |c| {
+                    ['k', 'm', 'g'].contains(&c.to_ascii_lowercase())
+                }),
+            ),
+            |(num_s, quant)| {
+                Ok(match (num_s.parse::<u64>(), quant.to_ascii_lowercase()) {
+                    (Ok(num), 'k') => num * 1000,
+                    (Ok(num), 'm') => num * 1000_000,
+                    (Ok(num), 'g') => num * 1000_000_000,
+                    _ => return Err(num_s),
+                })
+            },
+        )
+    }
+
+    pub fn parse_sieve_integer_operator<'a>() -> impl Parser<'a, (IntegerOperator, u64)> {
+        move |input| {
+            ws(pair(
+                either(
+                    literal_map(":over", IntegerOperator::Over),
+                    literal_map(":under", IntegerOperator::Under),
+                ),
+                ws(number()),
+            ))
+            .parse(input)
+        }
+    }
+    // ":comparator" <comparator-name: string>
+    pub fn parse_sieve_comparator<'a>() -> impl Parser<'a, CharacterOperator> {
+        move |input| {
+            ws(right(
+                parse_token(":comparator"),
+                ws(map_res(string(), |s| {
+                    if s == "i;octet" {
+                        Ok(CharacterOperator::Octet)
+                    } else if s == "i;ascii-casemap" {
+                        Ok(CharacterOperator::AsciiCasemap)
+                    } else {
+                        Err("invalid comparator")
+                    }
+                })),
+            ))
+            .parse(input)
+        }
+    }
+
+    // MATCH-TYPE   = ":is" / ":contains" / ":matches"
+    pub fn parse_sieve_match_type<'a>() -> impl Parser<'a, MatchOperator> {
+        move |input| {
+            either(
+                map(parse_token(":is"), |_| MatchOperator::Is),
+                either(
+                    map(parse_token(":contains"), |_| MatchOperator::Contains),
+                    map(parse_token(":matches"), |_| MatchOperator::Matches),
+                ),
+            )
+            .parse(input)
+        }
+    }
+
+    /* string-list  = "[" string *("," string) "]" / string
+                    ; if there is only a single string, the brackets
+                    ; are optional
+    */
+    pub fn parse_string_list<'a>() -> impl Parser<'a, Vec<String>> {
+        move |input| {
+            either(
+                delimited(
+                    ws(parse_token("[")),
+                    separated_list0(string(), ws(parse_token(",")), false),
+                    ws(parse_token("]")),
+                ),
+                map(string(), |s| vec![s]),
+            )
+            .parse(input)
+        }
+    }
+
+    /* Usage:   header [COMPARATOR] [MATCH-TYPE]
+     * <header-names: string-list> <key-list: string-list>
+     */
+    pub fn parse_sieve_header<'a>() -> impl Parser<'a, ConditionRule> {
+        move |input| {
+            map(
+                ws(pair(
+                    right(parse_token("header"), move |input| {
+                        crate::permutation! {
+                            input,
+                            comparator, Option<CharacterOperator>, opt(parse_sieve_comparator()),
+                            match_type, Option<MatchOperator>, opt(parse_sieve_match_type())
+                        }
+                    }),
+                    pair(ws(parse_string_list()), ws(parse_string_list())),
+                )),
+                |((comparator, match_operator), (header_names, key_list))| ConditionRule::Header {
+                    comparator,
+                    match_operator,
+                    header_names,
+                    key_list,
+                },
+            )
+            .parse(input)
+        }
+    }
+
+    // ADDRESS-PART = ":localpart" / ":domain" / ":all"
+    pub fn parse_sieve_address_type<'a>() -> impl Parser<'a, AddressOperator> {
+        move |input| {
+            either(
+                map(parse_token(":localpart"), |_| AddressOperator::Localpart),
+                either(
+                    map(parse_token(":domain"), |_| AddressOperator::Domain),
+                    map(parse_token(":all"), |_| AddressOperator::All),
+                ),
+            )
+            .parse(input)
+        }
+    }
+
+    // address [COMPARATOR] [ADDRESS-PART] [MATCH-TYPE] <header-list: string-list> <key-list: string-list>
+    pub fn parse_sieve_address<'a>() -> impl Parser<'a, ConditionRule> {
+        move |input| {
+            map(
+                ws(pair(
+                    right(parse_token("address"), move |input| {
+                        crate::permutation! {
+                            input,
+                            match_type, Option<MatchOperator>, opt(parse_sieve_match_type()),
+                            comparator, Option<CharacterOperator>, opt(parse_sieve_comparator()),
+                            address_type, Option<AddressOperator>, opt(parse_sieve_address_type())
+                        }
+                    }),
+                    pair(ws(parse_string_list()), ws(parse_string_list())),
+                )),
+                |((match_type, comparator, address_part), (header_list, key_list))| {
+                    ConditionRule::Address {
+                        comparator,
+                        address_part,
+                        match_type,
+                        header_list,
+                        key_list,
+                    }
+                },
+            )
+            .parse(input)
+        }
+    }
+
+    pub fn parse_sieve_test<'a>() -> impl Parser<'a, ConditionRule> {
+        move |input| {
+            either(
+                either(
+                    literal_map("true", ConditionRule::Literal(true)),
+                    literal_map("false", ConditionRule::Literal(false)),
+                ),
+                either(
+                    either(
+                        map(
+                            right(ws(parse_token("exists")), ws(parse_string_list())),
+                            |l| ConditionRule::Exists(l),
+                        ),
+                        map(
+                            right(ws(parse_token("size")), ws(parse_sieve_integer_operator())),
+                            |(operator, limit)| ConditionRule::Size { operator, limit },
+                        ),
+                    ),
+                    either(
+                        either(
+                            map(right(ws(parse_token("not")), parse_sieve_test()), |cond| {
+                                ConditionRule::Not(Box::new(cond))
+                            }),
+                            either(parse_sieve_header(), parse_sieve_address()),
+                        ),
+                        either(
+                            map(right(ws(parse_token("allof")), parse_test_list()), |l| {
+                                ConditionRule::AllOf(l)
+                            }),
+                            map(right(ws(parse_token("anyof")), parse_test_list()), |l| {
+                                ConditionRule::AnyOf(l)
+                            }),
+                        ),
+                    ),
+                ),
+            )
+            .parse(input)
+        }
+    }
+
+    /* test-list  = "(" test *("," test) ")"
+     */
+    pub fn parse_test_list<'a>() -> impl Parser<'a, Vec<ConditionRule>> {
+        move |input| {
+            delimited(
+                ws(parse_token("(")),
+                separated_list0(ws(parse_sieve_test()), ws(parse_token(",")), false),
+                ws(parse_token(")")),
+            )
+            .parse(input)
+        }
+    }
+
+    pub fn parse_sieve_rule<'a>() -> impl Parser<'a, Rule> {
+        either(
+            map(
+                either(
+                    either(parse_sieve_stop(), parse_sieve_require()),
+                    parse_sieve_if(),
+                ),
+                |c| Rule::Control(c),
+            ),
+            map(
+                either(
+                    either(parse_sieve_keep(), parse_sieve_fileinto()),
+                    either(parse_sieve_redirect(), parse_sieve_discard()),
+                ),
+                |ac| Rule::Action(ac),
+            ),
+        )
+    }
+
+    pub fn parse_sieve_block<'a>() -> impl Parser<'a, RuleBlock> {
+        move |input| {
+            map(
+                ws(delimited(
+                    parse_token("{"),
+                    ws(zero_or_more(parse_sieve_rule())),
+                    parse_token("}"),
+                )),
+                |v| RuleBlock(v),
+            )
+            .parse(input)
+        }
+    }
+
+    pub fn parse_sieve_if<'a>() -> impl Parser<'a, ControlCommand> {
+        either(
+            map(
+                pair(
+                    parse_sieve_if_bare(),
+                    ws(right(parse_token("else"), ws(parse_sieve_block()))),
+                ),
+                |(ifbare, else_)| match ifbare {
+                    ControlCommand::If {
+                        condition,
+                        elsif,
+                        else_: _,
+                    } => ControlCommand::If {
+                        condition,
+                        elsif,
+                        else_: Some(else_),
+                    },
+                    _ => unreachable!(),
+                },
+            ),
+            parse_sieve_if_bare(),
+        )
+    }
+
+    pub fn parse_sieve_if_bare<'a>() -> impl Parser<'a, ControlCommand> {
+        either(
+            map(
+                pair(
+                    ws(pair(
+                        ws(right(parse_token("if"), ws(parse_sieve_test()))),
+                        ws(parse_sieve_block()),
+                    )),
+                    ws(pair(
+                        ws(right(parse_token("elsif"), ws(parse_sieve_test()))),
+                        ws(parse_sieve_block()),
+                    )),
+                ),
+                |(condition, elsif)| ControlCommand::If {
+                    condition,
+                    elsif: Some(elsif),
+                    else_: None,
+                },
+            ),
+            map(
+                pair(
+                    ws(right(parse_token("if"), ws(parse_sieve_test()))),
+                    ws(parse_sieve_block()),
+                ),
+                |(cond, block)| ControlCommand::If {
+                    condition: (cond, block),
+                    elsif: None,
+                    else_: None,
+                },
+            ),
+        )
+    }
+
+    pub fn parse_sieve_require<'a>() -> impl Parser<'a, ControlCommand> {
+        move |input| {
+            right(
+                ws(parse_token("require")),
+                ws(left(
+                    map(parse_string_list(), |string_list| {
+                        ControlCommand::Require(string_list)
+                    }),
+                    ws(parse_token(";")),
+                )),
+            )
+            .parse(input)
+        }
+    }
+
+    pub fn parse_sieve<'a>() -> impl Parser<'a, Vec<Rule>> {
+        ws(zero_or_more(ws(parse_sieve_rule())))
+    }
+}
+
+#[cfg(test)]
+mod test {
+    use super::parser::*;
+    use crate::parsec::Parser;
+
+    use super::ActionCommand::*;
+    use super::AddressOperator::*;
+    use super::CharacterOperator::*;
+    use super::ConditionRule::*;
+    use super::ControlCommand::*;
+    use super::IntegerOperator::*;
+    use super::MatchOperator::*;
+    use super::Rule::*;
+    use super::RuleBlock;
+
+    #[test]
+    fn test_sieve_parse_strings() {
+        assert_eq!(
+            Ok(("", vec!["fileinto".to_string(), "reject".to_string()])),
+            parse_string_list().parse(r#"["fileinto", "reject"]"#)
+        );
+
+        assert_eq!(
+            Ok(("", vec!["fileinto".to_string()])),
+            parse_string_list().parse(r#""fileinto""#)
+        );
+    }
+
+    #[test]
+    fn test_sieve_parse_conditionals() {
+        /* Operators that start with : like :matches are unordered and optional, since they have
+         * defaults. But that means we must handle any order correctly, which is tricky if we use
+         * an optional parser; for an optional parser both None and Some(_) are valid values.
+         */
+
+        /* Permutations of two */
+        let raw_input = r#"header :contains :comparator "i;octet" "Subject"
+                   "MAKE MONEY FAST""#;
+        let (_, first) = parse_sieve_test().parse(raw_input).unwrap();
+        assert_eq!(
+            Header {
+                comparator: Some(Octet),
+                match_operator: Some(Contains),
+                header_names: ["Subject".to_string()].to_vec(),
+                key_list: ["MAKE MONEY FAST".to_string()].to_vec()
+            },
+            first
+        );
+
+        let raw_input = r#"header :comparator "i;octet" :contains "Subject"
+                   "MAKE MONEY FAST""#;
+        assert_eq!(Ok(("", first)), parse_sieve_test().parse(raw_input));
+
+        /* Permutations of three */
+        let raw_input = r#"address :DOMAIN :comparator "i;octet" :is ["From", "To"] "example.com""#;
+        let (_, first) = parse_sieve_test().parse(raw_input).unwrap();
+
+        assert_eq!(
+            &Address {
+                comparator: Some(Octet),
+                address_part: Some(Domain),
+                match_type: Some(Is),
+                header_list: ["From".to_string(), "To".to_string()].to_vec(),
+                key_list: ["example.com".to_string()].to_vec()
+            },
+            &first
+        );
+
+        let raw_input =
+            r#"address :DOMAIN :is :comparator "i;octet"  ["From", "To"] "example.com""#;
+        assert_eq!(Ok(("", first.clone())), parse_sieve_test().parse(raw_input));
+
+        let raw_input =
+            r#"address :is :DOMAIN :comparator "i;octet"  ["From", "To"] "example.com""#;
+        assert_eq!(Ok(("", first.clone())), parse_sieve_test().parse(raw_input));
+
+        let raw_input = r#"address :is :comparator "i;octet" :DOMAIN ["From", "To"] "example.com""#;
+        assert_eq!(Ok(("", first)), parse_sieve_test().parse(raw_input));
+    }
+
+    #[test]
+    fn test_sieve_parse_ifs() {
+        let raw_input = "if true {\nstop ;\n}";
+        assert_eq!(
+            Ok((
+                "",
+                Control(If {
+                    condition: (Literal(true), RuleBlock([Control(Stop)].to_vec())),
+                    elsif: None,
+                    else_: None
+                })
+            )),
+            parse_sieve_rule().parse(raw_input)
+        );
+
+        let raw_input = r#"# Reject all messages that contain the string "ivnten"in the Subject.
+if header :contains "subject" "ivnten"
+{
+    discard;
+} else {
+    keep;
+}"#;
+
+        assert_eq!(
+            Ok((
+                "",
+                [Control(If {
+                    condition: (
+                        Header {
+                            comparator: None,
+                            match_operator: Some(Contains),
+                            header_names: ["subject".to_string()].to_vec(),
+                            key_list: ["ivnten".to_string()].to_vec()
+                        },
+                        RuleBlock([Action(Discard)].to_vec())
+                    ),
+                    elsif: None,
+                    else_: Some(RuleBlock([Action(Keep)].to_vec()))
+                })]
+                .to_vec()
+            )),
+            parse_sieve().parse(raw_input)
+        );
+
+        let raw_input = r#"# Reject all messages that contain the string "ivnten"in the Subject.
+if header :contains "subject" "ivnten"
+{
+    discard;
+}
+# Silently discard all messages sent from the tax man
+elsif address :matches :domain "from" "*hmrc.gov.uk"
+{
+    keep;
+}"#;
+        assert_eq!(
+            Ok((
+                "",
+                [Control(If {
+                    condition: (
+                        Header {
+                            comparator: None,
+                            match_operator: Some(Contains),
+                            header_names: ["subject".to_string()].to_vec(),
+                            key_list: ["ivnten".to_string()].to_vec()
+                        },
+                        RuleBlock([Action(Discard)].to_vec())
+                    ),
+                    elsif: Some((
+                        Address {
+                            comparator: None,
+                            address_part: Some(Domain),
+                            match_type: Some(Matches),
+                            header_list: ["from".to_string()].to_vec(),
+                            key_list: ["*hmrc.gov.uk".to_string()].to_vec()
+                        },
+                        RuleBlock([Action(Keep)].to_vec())
+                    )),
+                    else_: None
+                })]
+                .to_vec()
+            )),
+            parse_sieve().parse(raw_input)
+        );
+    }
+
+    #[test]
+    fn test_sieve_parse() {
+        let raw_input = r#"# The hash character starts a one-line comment.
+
+"#;
+        assert_eq!(Ok(("", vec![])), parse_sieve().parse(raw_input));
+
+        let raw_input = r#"# The hash character starts a one-line comment.
+# Everything after a # character until the end of line is ignored.
+
+/* this is a bracketed (C-style) comment. This type of comment can stretch
+ * over many lines. A bracketed comment begins with a forward slash, followed
+ * by an asterisk and ends with the inverse sequence: an asterisk followed
+ * by a forward slash. */
+"#;
+
+        assert_eq!(Ok(("", vec![])), parse_sieve().parse(raw_input));
+        // Test Lists (allof, anyof)
+
+        let raw_input = r#"# This test checks against Spamassassin's header fields:
+# If the spam level is 4 or more and the Subject contains too
+# many illegal characters, then silently discard the mail.
+if allof (header :contains "X-Spam-Level" "****",
+          header :contains "X-Spam-Report" "FROM_ILLEGAL_CHARS")
+{
+    discard;
+}
+# Discard mails that do not have a Date: or From: header field
+# or mails that are sent from the marketing department at example.com.
+elsif anyof (not exists ["from", "date"],
+        header :contains "from" "marketing@example.com") {
+    discard;
+}"#;
+
+        assert_eq!(
+            Ok((
+                "",
+                [Control(If {
+                    condition: (
+                        AllOf(
+                            [
+                                Header {
+                                    comparator: None,
+                                    match_operator: Some(Contains),
+                                    header_names: ["X-Spam-Level".to_string()].to_vec(),
+                                    key_list: ["****".to_string()].to_vec()
+                                },
+                                Header {
+                                    comparator: None,
+                                    match_operator: Some(Contains),
+                                    header_names: ["X-Spam-Report".to_string()].to_vec(),
+                                    key_list: ["FROM_ILLEGAL_CHARS".to_string()].to_vec()
+                                }
+                            ]
+                            .to_vec()
+                        ),
+                        RuleBlock([Action(Discard)].to_vec())
+                    ),
+                    elsif: Some((
+                        AnyOf(
+                            [
+                                Not(Box::new(Exists(
+                                    ["from".to_string(), "date".to_string()].to_vec()
+                                ))),
+                                Header {
+                                    comparator: None,
+                                    match_operator: Some(Contains),
+                                    header_names: ["from".to_string()].to_vec(),
+                                    key_list: ["marketing@example.com".to_string()].to_vec()
+                                }
+                            ]
+                            .to_vec()
+                        ),
+                        RuleBlock([Action(Discard)].to_vec())
+                    )),
+                    else_: None
+                })]
+                .to_vec()
+            )),
+            parse_sieve().parse(raw_input)
+        );
+        // Filter on message size
+        let raw_input = r#"# Delete messages greater than half a MB
+if size :over 500K
+{
+    discard;
+}
+# Also delete small mails, under 1k
+if size :under 1k
+{
+    discard;
+}"#;
+        assert_eq!(
+            Ok((
+                "",
+                [
+                    Control(If {
+                        condition: (
+                            Size {
+                                operator: Over,
+                                limit: 500000
+                            },
+                            RuleBlock([Action(Discard)].to_vec())
+                        ),
+                        elsif: None,
+                        else_: None
+                    }),
+                    Control(If {
+                        condition: (
+                            Size {
+                                operator: Under,
+                                limit: 1000
+                            },
+                            RuleBlock([Action(Discard)].to_vec())
+                        ),
+                        elsif: None,
+                        else_: None
+                    })
+                ]
+                .to_vec()
+            )),
+            parse_sieve().parse(raw_input)
+        );
+
+        assert_eq!(
+            Ok((
+                "",
+                [
+                    Control(Require(["fileinto".to_string()].to_vec())),
+                    Control(If {
+                        condition: (
+                            Header {
+                                comparator: None,
+                                match_operator: Some(Contains),
+                                header_names: ["from".to_string()].to_vec(),
+                                key_list: ["coyote".to_string()].to_vec()
+                            },
+                            RuleBlock([Action(Discard)].to_vec())
+                        ),
+                        elsif: Some((
+                            Header {
+                                comparator: None,
+                                match_operator: Some(Contains),
+                                header_names: ["subject".to_string()].to_vec(),
+                                key_list: ["$$$".to_string()].to_vec()
+                            },
+                            RuleBlock([Action(Discard)].to_vec())
+                        )),
+                        else_: Some(RuleBlock(
+                            [Action(Fileinto {
+                                mailbox: "INBOX".to_string()
+                            })]
+                            .to_vec()
+                        ))
+                    })
+                ]
+                .to_vec()
+            )),
+            parse_sieve().parse(
+                r#"require "fileinto";
+             if header :contains "from" "coyote" {
+                discard;
+             } elsif header :contains ["subject"] ["$$$"] {
+                discard;
+             } else {
+                fileinto "INBOX";
+             }"#
+            )
+        );
+    }
+}