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Building E-mail messages in Rust

- 1 min read
Mauro D.
Mauro D.
Project Maintainer

Using mail-builder is straightforward:

        // Build a simple text message with a single attachment
        let mut message = MessageBuilder::new();
        message.from(("John Doe", "[email protected]"));
        message.to("[email protected]");
        message.subject("Hello, world!");
        message.text_body("Message contents go here.");
        message.binary_attachment("image/png", "image.png", &[1, 2, 3, 4]);


        // Write message to memory
        let mut output = Vec::new();
        message.write_to(&mut output).unwrap();

More complex messages with grouped addresses, inline parts and multipart/alternative sections can also be easily built:

        // Build a multipart message with text and HTML bodies,
        // inline parts and attachments.
        let mut message = MessageBuilder::new();
        message.from(("John Doe", "[email protected]"));


        // To recipients
        message.to(vec![
            ("Antoine de Saint-Exupéry", "[email protected]"),
            ("안녕하세요 세계", "[email protected]"),
            ("Xin chào", "[email protected]"),
        ]);


        // BCC recipients using grouped addresses
        message.bcc(vec![
            (
                "My Group",
                vec![
                    ("ASCII name", "[email protected]"),
                    ("ハロー・ワールド", "[email protected]"),
                    ("áéíóú", "[email protected]"),
                    ("Γειά σου Κόσμε", "[email protected]"),
                ],
            ),
            (
                "Another Group",
                vec![
                    ("שלום עולם", "[email protected]"),
                    ("ñandú come ñoquis", "[email protected]"),
                    ("Recipient", "[email protected]"),
                ],
            ),
        ]);


        // Set RFC and custom headers
        message.subject("Testing multipart messages");
        message.in_reply_to(vec!["message-id-1", "message-id-2"]);
        message.header("List-Archive", URL::new("http://example.com/archive"));


        // Set HTML and plain text bodies
        message.text_body("This is the text body!\n");
        message.html_body("<p>HTML body with <img src=\"cid:my-image\"/>!</p>");


        // Include an embedded image as an inline part
        message.binary_inline("image/png", "cid:my-image", &[0, 1, 2, 3, 4, 5]);


        // Add a text and a binary attachment
        message.text_attachment("text/plain", "my fíle.txt", "Attachment contents go here.");
        message.binary_attachment(
            "text/plain",
            "ハロー・ワールド",
            b"Binary contents go here.",
        );


        // Write the message to a file
        message
            .write_to(File::create("message.eml").unwrap())
            .unwrap();

Nested MIME body structures can be created using the body method:

    // Build a nested multipart message
        let mut message = MessageBuilder::new();


        message.from(Address::new_address("John Doe".into(), "[email protected]"));
        message.to(Address::new_address("Jane Doe".into(), "[email protected]"));
        message.subject("Nested multipart message");


        // Define the nested MIME body structure
        message.body(MimePart::new_multipart(
            "multipart/mixed",
            vec![
                MimePart::new_text("Part A contents go here...").inline(),
                MimePart::new_multipart(
                    "multipart/mixed",
                    vec![
                        MimePart::new_multipart(
                            "multipart/alternative",
                            vec![
                                MimePart::new_multipart(
                                    "multipart/mixed",
                                    vec![
                                        MimePart::new_text("Part B contents go here...").inline(),
                                        MimePart::new_binary(
                                            "image/jpeg",
                                            "Part C contents go here...".as_bytes(),
                                        )
                                        .inline(),
                                        MimePart::new_text("Part D contents go here...").inline(),
                                    ],
                                ),
                                MimePart::new_multipart(
                                    "multipart/related",
                                    vec![
                                        MimePart::new_html("Part E contents go here...").inline(),
                                        MimePart::new_binary(
                                            "image/jpeg",
                                            "Part F contents go here...".as_bytes(),
                                        ),
                                    ],
                                ),
                            ],
                        ),
                        MimePart::new_binary("image/jpeg", "Part G contents go here...".as_bytes())
                            .attachment("image_G.jpg"),
                        MimePart::new_binary(
                            "application/x-excel",
                            "Part H contents go here...".as_bytes(),
                        ),
                        MimePart::new_binary(
                            "x-message/rfc822",
                            "Part J contents go here...".as_bytes(),
                        ),
                    ],
                ),
                MimePart::new_text("Part K contents go here...").inline(),
            ],
        ));


        // Write the message to a file
        message
            .write_to(File::create("nested-message.eml").unwrap())
            .unwrap();

The library is available at https://crates.io/crates/mail-builder and the documentation at https://docs.rs/mail-builder.

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