limit messages number
Inspired by a comment from Phil Pennock on the SAGE mailing list:
I really wish that I'd be allowed to put a per-customer throttle on mails-per-day, raisable if a customer has legitimate reasons to be sending mail ...
High email volumes are often generated by a compromised account.
They can damage your company’s reputation and the one of your mailserver.
The “limit message number” option lets you define a maximum number of daily emails per sender,
so that any excess quantities will be blocked before going on the internet.
The sending of “extra quantity” communications are stopped.
The emails get bounced back immediately to the sender, with a warning like:
An error occurred when sending email. The mail server answered: 450 4.7.1 <>... firstname.lastname@example.org has exceeded n messages per 1 day.