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 <>...  sender@example.com has exceeded n messages per 1 day.

As an antispam measure, most smtp servers introduced an option to limit the number of recipients
that can be specified for a given envelope. In Sendmail it is Called “MaxRecipientsPerMessage”.

RealSender promotes the limit on the number of recipients per message,
to reduce abuses and to avoid the risk of sending cc/bcc to many addresses.

We share a list of 300 @bogusemail.net addresses for testing:
bogusemail-test.txt

The messages will reach a “black-hole” mailserver.

You can use them at your convenience,
to check how many recipients per message
your smtp server allows the sending to.