mikel/mail

Mail is a Ruby library for working with email: composing messages, sending them, receiving them, and parsing them. It is written entirely in Ruby and is widely used as a foundation for email handling in Ruby web applications, including as the default mail library behind Ruby on Rails. The library gives developers a straightforward way to construct email messages in code. You can set the from address, recipients, subject, and body through a clean block-based syntax, or by assigning fields one at a time. It handles both plain text and HTML emails, supports attachments, and can build multipart messages that include both a text and an HTML version in one email so the recipient's email client can display whichever it supports. Beyond composing messages, the library can parse incoming raw email text back into structured objects, so you can read specific headers, access attachments, or extract the body. It follows the relevant internet standards (RFC 5322 for email format and RFC 2045-2049 for multipart messages), which means it can handle the wide variety of email formats found in the real world. Rather than crashing when it encounters something unexpected, it skips the problematic part and continues parsing. Sending email is done through adapters for SMTP and POP3, the two common protocols for outgoing and incoming mail. The library also provides a test delivery mode that captures sent mail in memory rather than actually sending it, which is useful during development and automated testing. Character encoding in email is historically complicated because different email systems and languages handle text differently. The library addresses this by providing explicit encoded and decoded methods on all message components so developers have predictable control over what gets sent versus what gets read. The project is open source, tested against multiple Ruby versions, and licensed under the MIT license.