mail-parser

mail-parser is an e-mail parsing library written in Rust that fully conforms to the Internet Message Format standard (RFC 5322), the Multipurpose Internet Mail Extensions (MIME; RFC 2045 - 2049) as well as many other internet messaging RFCs.

It also supports decoding messages in 41 different character sets including obsolete formats such as UTF-7. All Unicode (UTF-*) and single-byte character sets are handled internally by the library while support for legacy multi-byte encodings of Chinese and Japanese languages such as BIG5 or ISO-2022-JP is provided by the optional dependency encoding_rs.

In general, this library abides by the Postel's law or Robustness Principle which states that an implementation must be conservative in its sending behavior and liberal in its receiving behavior. This means that mail-parser will make a best effort to parse non-conformant e-mail messages as long as these do not deviate too much from the standard.

Unlike other e-mail parsing libraries that return nested representations of the different MIME parts in a message, this library conforms to RFC 8621, Section 4.1.4 and provides a more human-friendly representation of the message contents consisting of just text body parts, html body parts and attachments. Additionally, conversion to/from HTML and plain text inline body parts is done automatically when the alternative version is missing.

Performance and memory safety were two important factors while designing mail-parser:

• Zero-copy: Practically all strings returned by this library are Cow<str> references to the input raw message.
• High performance Base64 decoding based on Chromium's decoder (the fastest non-SIMD decoder).
• Fast parsing of message header fields, character set names and HTML entities using perfect hashing.
• Written in 100% safe Rust with no external dependencies.
• Every function in the library has been fuzzed and thoroughly tested with MIRI.
• Battle-tested with millions of real-world e-mail messages dating from 1995 until today.
• Used in production environments worldwide by Stalwart Mail Server.

Usage Example

    let input = br#"From: Art Vandelay <art@vandelay.com> (Vandelay Industries)
To: "Colleagues": "James Smythe" <james@vandelay.com>; Friends:
    jane@example.com, =?UTF-8?Q?John_Sm=C3=AEth?= <john@example.com>;
Date: Sat, 20 Nov 2021 14:22:01 -0800
Subject: Why not both importing AND exporting? =?utf-8?b?4pi6?=
Content-Type: multipart/mixed; boundary="festivus";

--festivus
Content-Type: text/html; charset="us-ascii"
Content-Transfer-Encoding: base64

PGh0bWw+PHA+SSB3YXMgdGhpbmtpbmcgYWJvdXQgcXVpdHRpbmcgdGhlICZsZHF1bztle
HBvcnRpbmcmcmRxdW87IHRvIGZvY3VzIGp1c3Qgb24gdGhlICZsZHF1bztpbXBvcnRpbm
cmcmRxdW87LDwvcD48cD5idXQgdGhlbiBJIHRob3VnaHQsIHdoeSBub3QgZG8gYm90aD8
gJiN4MjYzQTs8L3A+PC9odG1sPg==
--festivus
Content-Type: message/rfc822

From: "Cosmo Kramer" <kramer@kramerica.com>
Subject: Exporting my book about coffee tables
Content-Type: multipart/mixed; boundary="giddyup";

--giddyup
Content-Type: text/plain; charset="utf-16"
Content-Transfer-Encoding: quoted-printable

=FF=FE=0C!5=D8"=DD5=D8)=DD5=D8-=DD =005=D8*=DD5=D8"=DD =005=D8"=
=DD5=D85=DD5=D8-=DD5=D8,=DD5=D8/=DD5=D81=DD =005=D8*=DD5=D86=DD =
=005=D8=1F=DD5=D8,=DD5=D8,=DD5=D8(=DD =005=D8-=DD5=D8)=DD5=D8"=
=DD5=D8=1E=DD5=D80=DD5=D8"=DD!=00
--giddyup
Content-Type: image/gif; name*1="about "; name*0="Book ";
              name*2*=utf-8''%e2%98%95 tables.gif
Content-Transfer-Encoding: Base64
Content-Disposition: attachment

R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7
--giddyup--
--festivus--
"#;

    let message = MessageParser::default().parse(input).unwrap();

    // Parses addresses (including comments), lists and groups
    assert_eq!(
        message.from().unwrap().first().unwrap(),
        &Addr::new(
            "Art Vandelay (Vandelay Industries)".into(),
            "art@vandelay.com"
        )
    );

    assert_eq!(
        message.to().unwrap().as_group().unwrap(),
        &[
            Group::new(
                "Colleagues",
                vec![Addr::new("James Smythe".into(), "james@vandelay.com")]
            ),
            Group::new(
                "Friends",
                vec![
                    Addr::new(None, "jane@example.com"),
                    Addr::new("John Smîth".into(), "john@example.com"),
                ]
            )
        ]
    );

    assert_eq!(
        message.date().unwrap().to_rfc3339(),
        "2021-11-20T14:22:01-08:00"
    );

    // RFC2047 support for encoded text in message readers
    assert_eq!(
        message.subject().unwrap(),
        "Why not both importing AND exporting? ☺"
    );

    // HTML and text body parts are returned conforming to RFC8621, Section 4.1.4
    assert_eq!(
        message.body_html(0).unwrap(),
        concat!(
            "<html><p>I was thinking about quitting the &ldquo;exporting&rdquo; to ",
            "focus just on the &ldquo;importing&rdquo;,</p><p>but then I thought,",
            " why not do both? &#x263A;</p></html>"
        )
    );

    // HTML parts are converted to plain text (and viceversa) when missing
    assert_eq!(
        message.body_text(0).unwrap(),
        concat!(
            "I was thinking about quitting the “exporting” to focus just on the",
            " “importing”,\nbut then I thought, why not do both? ☺\n"
        )
    );

    // Supports nested messages as well as multipart/digest
    let nested_message = message
        .attachment(0)
        .unwrap()
        .message();
        .unwrap();

    assert_eq!(
        nested_message.subject().unwrap(),
        "Exporting my book about coffee tables"
    );

    // Handles UTF-* as well as many legacy encodings
    assert_eq!(
        nested_message.body_text(0).unwrap(),
        "ℌ𝔢𝔩𝔭 𝔪𝔢 𝔢𝔵𝔭𝔬𝔯𝔱 𝔪𝔶 𝔟𝔬𝔬𝔨 𝔭𝔩𝔢𝔞𝔰𝔢!"
    );
    assert_eq!(
        nested_message.body_html(0).unwrap(),
        "<html><body>ℌ𝔢𝔩𝔭 𝔪𝔢 𝔢𝔵𝔭𝔬𝔯𝔱 𝔪𝔶 𝔟𝔬𝔬𝔨 𝔭𝔩𝔢𝔞𝔰𝔢!</body></html>"
    );

    let nested_attachment = nested_message.attachment(0).unwrap();

    assert_eq!(nested_attachment.len(), 42);

    // Full RFC2231 support for continuations and character sets
    assert_eq!(
        nested_attachment.attachment_name().unwrap(),
        "Book about ☕ tables.gif"
    );

    // Integrates with Serde
    println!("{}", serde_json::to_string_pretty(&message).unwrap());

More examples available under the examples directory. Please note that this library does not support building e-mail messages as this functionality is provided separately by the mail-builder crate.

Testing, Fuzzing & Benchmarking

To run the testsuite:

 $ cargo test --all-features

or, to run the testsuite with MIRI:

 $ cargo +nightly miri test --all-features

To fuzz the library with cargo-fuzz:

 $ cargo +nightly fuzz run mail_parser

and, to run the benchmarks:

 $ cargo +nightly bench --all-features

Conformed RFCs

• RFC 822 - Standard for ARPA Internet Text Messages
• RFC 5322 - Internet Message Format
• RFC 2045 - Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies
• RFC 2046 - Multipurpose Internet Mail Extensions (MIME) Part Two: Media Types
• RFC 2047 - MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text
• RFC 2048 - Multipurpose Internet Mail Extensions (MIME) Part Four: Registration Procedures
• RFC 2049 - Multipurpose Internet Mail Extensions (MIME) Part Five: Conformance Criteria and Examples
• RFC 2231 - MIME Parameter Value and Encoded Word Extensions: Character Sets, Languages, and Continuations
• RFC 2557 - MIME Encapsulation of Aggregate Documents, such as HTML (MHTML)
• RFC 2183 - Communicating Presentation Information in Internet Messages: The Content-Disposition Header Field
• RFC 2392 - Content-ID and Message-ID Uniform Resource Locators
• RFC 3282 - Content Language Headers
• RFC 6532 - Internationalized Email Headers
• RFC 2152 - UTF-7 - A Mail-Safe Transformation Format of Unicode
• RFC 2369 - The Use of URLs as Meta-Syntax for Core Mail List Commands and their Transport through Message Header Fields
• RFC 2919 - List-Id: A Structured Field and Namespace for the Identification of Mailing Lists
• RFC 3339 - Date and Time on the Internet: Timestamps
• RFC 8621 - The JSON Meta Application Protocol (JMAP) for Mail (Section 4.1.4)
• RFC 5957 - Internet Message Access Protocol - SORT and THREAD Extensions (Section 2.1)

Supported Character Sets

• UTF-8
• UTF-16, UTF-16BE, UTF-16LE
• UTF-7
• US-ASCII
• ISO-8859-1
• ISO-8859-2
• ISO-8859-3
• ISO-8859-4
• ISO-8859-5
• ISO-8859-6
• ISO-8859-7
• ISO-8859-8
• ISO-8859-9
• ISO-8859-10
• ISO-8859-13
• ISO-8859-14
• ISO-8859-15
• ISO-8859-16
• CP1250
• CP1251
• CP1252
• CP1253
• CP1254
• CP1255
• CP1256
• CP1257
• CP1258
• KOI8-R
• KOI8_U
• MACINTOSH
• IBM850
• TIS-620

Supported character sets via the optional dependency encoding_rs:

• SHIFT_JIS
• BIG5
• EUC-JP
• EUC-KR
• GB18030
• GBK
• ISO-2022-JP
• WINDOWS-874
• IBM-866

License

Licensed under either of

• Apache License, Version 2.0 (LICENSE-APACHE or http://www.apache.org/licenses/LICENSE-2.0)
• MIT license (LICENSE-MIT or http://opensource.org/licenses/MIT)

at your option.

Copyright

Copyright (C) 2020-2022, Stalwart Labs Ltd.