Neither of the two libraries listed have a way to validate a string for RFC 5321 compliance.
Let's not break people's code for no reason, especially for a module which causes no one any trouble.
Comment #2 by doob — 2017-02-22T08:02:34Z
(In reply to greenify from comment #0)
> Very old module and only a port of the C module.
>
> This can be done a lot better via DUB packages, e.g.
>
> -> https://github.com/anton-dutov/mail
> -> http://vibed.org/api/vibe.mail.smtp/Mail
>
> Proposed action: deprecate and move to undeaD
It's actually ported from PHP, by request from Walter (or Andrei).