Passkey Credentials

April 27, 2025 permalink

(Rust) a milter that automatically adds a List-Unsubscribe header to outbound emails.

https://github.com/arduent/passkey-credentials

Here's a milter in Rust that adds List-Unsubscribe headers. It creates a URL that has encoded email-from, rcpt-to and a HMAC SHA 256 verification hash using a shared secret key, that way the web server handling the post request doesn't have to live on the same server as the milter/smtp server.

What does this do? Well essentially it will put an unsubscribe link at the top of your email in clients like gmail (other mail handlers may do the same) like the image here, the blue link at the top. possibly it improves deliverability of newsletter and transactional emails.