mailmate

https://github.com/brianmd/mailmate

mailmate is a Ruby library and CLI for working with MailMate's on-disk storage and AppleScript surface. It includes a smart-mailbox filter engine (lexer/parser/evaluator over MailMate's filter language), readers for the binary header indexes, and CLI tools for searching, reading, modifying, and sending mail via MailMate. Requires macOS with MailMate installed. Some library pieces (parser, evaluator, fixture-driven tests) work on any platform; the integration pieces (AppleScript driver, filesystem readers) raise Mailmate::PlatformError on non-macOS hosts.