Andrzej Adam Filip wrote:
Tilman Schmidt <[email protected]> wrote:
Am 2009-11-23 21:38 schrieb -:
I too limit connections to one, and one per 5 minutes. Should
remotes violate that, they get two warnings (ICMP admin-prohibited),
and if they're too eager, they fall into my TCP TARPIT.
I wonder. Do you have any data on how typical mail server software
reacts to that sort of policy? What does, for example, a Sendmail or
Exchange server in default configuration do if it tries to deliver two
mails to a destination server, the first one succeeds, and the second
one fails with "administratively prohibited"?
AFAIK sendmail does not distinguish between reasons why establishing TCP
connection have failed. Have I missed something?
Any reasonable smtp mailer will handle a connection failure by retrying
any other MX listed in DNS and if none succeed, queuing for subsequent
retries. It doesn't make a lot of sense to limit at rates that that
aren't a threat to your service unless you have a dictionary attack with
mostly invalid recipients (which sendmail already knows how to
throttle). Otherwise you'll just back up mailing lists.
--
Les Mikesell
[email protected]
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