How do I throttle outbound email with sendmail?

Question

I know, I know, I should switch to Postfix. But in the meantime, how do I throttle outbound email (especially email to a single domain) in Sendmail?

Answer 1

Don't know how to do it in sendmail.

If it is mail to a single domain you want to throttle and you know the MX(s) for that domain only MX for that domain, I think you could use iptables rate limiting on that domain's MX(s) IP(s) and relevant ports, though I've never actually used iptables rate limiting myself for any purpose.

Most of the examples I've seen for iptables rate limiting are for incoming (INPUT chain) but I'd imagine it would work for outgoing too.