AxeSMTP is a toolkit, including applications, for modifying SMTP traffic while passing through.
DKIM Milter
SPF Milter
Multi-purpose security milter.
SpamAssassin Milter
Asynchronous milter library for Rust
libMilterPHP is a Postfix/Sendmail Milter library implementation in PHP.
Low-level Rust FFI bindings to libmilter
Rust bindings to the sendmail milter library