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I deal with a number of devices and applications that don't support SNMP traps for notification but do support email. The couple times I've been "mail-bombed" b

I deal with a number of devices and applications that don't support SNMP traps for notification but do support email. The couple times I've been "mail-bombed" by a device sending hundreds, thousands, or more notifications in a short period of time have been frustrating. Has anybody heard of a rate-limiting SMTP proxy or MTA? I've thought about writing such a thing, but I'd gladly use something already-developed. I'm thinking of a simple token-bucket that uses to/from (or perhaps to/from/subject) to limit duplicate notifications and/or collapse duplicates in a manner similar to a syslog daemon logging "Last message repeated xxx times".

Karrot_Kream 5y ago
Most MTAs have rate-limiting out of the box. Postfix, Courier, and OpenSMTPD have rate-limiting in-built, and though I'm less familiar with Qmail, there's probably patches to make Qmail work with rate limiting.
denton-scratch 5y ago
You don't need a proxy; Postfix can rate-limit natively. Plugins, "milters" and stuff inherited from Sendmail; and socket-level filters like Spamassassin, provide pretty-much comprehensive control. I agree that Postfix config is confusing. It beats the bejabers out of Sendmail config, but that's whataboutism. Dovecot config isn't that hard, unless you're trying to do hard stuff. Even then, your site config is an overlay on the default config, which should be what you get with your distro. The site-specific stuff is usually ony a couple of dozen lines. I expect you could also rig Postfix as a rate-limiting front-end for some inferior MTA :-) [Edit: oh - and Postfix/Dovecot doesn't need a machine to itself, if you're dealing with less than 20-or-so accounts, and you haven't set up a bot to spam the MTA. Actually, I think there are exactly zero circumstances in which a mailserver shouldn't be kicked-off the machine, in favour of a higher-priority job - email is a best-efforts, store-and-forward system]
- EvanAnderson 5y ago
  It looks like PostFWD would probably do what I want. I haven't had occasion to configure Postfix for much more than a small office plain vanilla MTA w/ a smart host for outbound in thr last few years. I really need to spend some quality time doing oddball things with it.

Karrot_Kream 5y ago

Most MTAs have rate-limiting out of the box. Postfix, Courier, and OpenSMTPD have rate-limiting in-built, and though I'm less familiar with Qmail, there's probably patches to make Qmail work with rate limiting.

denton-scratch 5y ago

You don't need a proxy; Postfix can rate-limit natively. Plugins, "milters" and stuff inherited from Sendmail; and socket-level filters like Spamassassin, provide pretty-much comprehensive control. I agree that Postfix config is confusing. It beats the bejabers out of Sendmail config, but that's whataboutism. Dovecot config isn't that hard, unless you're trying to do hard stuff. Even then, your site config is an overlay on the default config, which should be what you get with your distro. The site-specific stuff is usually ony a couple of dozen lines. I expect you could also rig Postfix as a rate-limiting front-end for some inferior MTA :-) [Edit: oh - and Postfix/Dovecot doesn't need a machine to itself, if you're dealing with less than 20-or-so accounts, and you haven't set up a bot to spam the MTA. Actually, I think there are exactly zero circumstances in which a mailserver shouldn't be kicked-off the machine, in favour of a higher-priority job - email is a best-efforts, store-and-forward system]

EvanAnderson 5y ago
It looks like PostFWD would probably do what I want. I haven't had occasion to configure Postfix for much more than a small office plain vanilla MTA w/ a smart host for outbound in thr last few years. I really need to spend some quality time doing oddball things with it.