postfix and rate limiting, sender control, etc

postfix has builtin controls restricting certain kinds of things, such as rate at which clients can connect, number of recipients per message, no. of connections per client, etc. These can be seen in man 8 smtpd and anvil.

As I didn't want to interfere too much with what might use the localhost instance, I added an instance of postfix listening on port 10025 of the eth0 address (192.168.10.208). That required adding a line to master.cf (I just added it under the standard smtp line):

192.168.10.208:10025 inet n - n - - smtpd
-o smtpd_client_message_rate_limit=5

The '-o smtpd_client_message_rate_limit=5' bit was to specify an override to limit connections from one client to 5 per the default anvil time (60s). The '-o' simply means override what is set in main.cf

The mail that I was attempting to restrict was being generated by snmpttd reading traps. It calls the 'mail' command for each trap, which can lead to a lot of mail in a large network. Now, the problem was that the 'mail' MUA (which is part of 'mailx' package in RHEL5) does not actually connect to smtp over tcp by default (and nor can I find any way of changing this in RHEL version, since all of the .mailrc and /etc/mail.rc directives, where you can specify smtp server and port, do not apply seemingly. They aren't in the man pages anyway. So I used the Mail::Sendmail module, which is easy to configure. BTW: I have not tried using '-o smtpd_client_message_rate_limit=5' on the 'unix' socket listening in master.cf, I assumed that it would not call smtpd, but that is because I was too lazy to read all the documentation on how postfix works ;)

Anyway, this works well