Email improvement: Ability to rate limit outgoing messages from the server & cap messages sent per domain in a given timeframe

[d19dotca]

It'd be great to allow the ability to rate limit messages (example: SMTP server can only send up to 10 messages per minute).

And heavily related to this request as well is to set message caps on domains for how much they can send per day (example: domain example.com can only send out 50 messages per day).

[d19dotca]

I just realized part of this is a duplicate of one that @marcusquinn filed earlier for Add a setting for sendmail limits per mailbox per day