postfix-users October 2010 archive
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postfix-users: Re: SMTP relay and greylisting

Re: SMTP relay and greylisting

From: Michael Orlitzky <michael_at_nospam>
Date: Tue Oct 26 2010 - 03:05:44 GMT

On 10/25/2010 10:38 PM, utahnix wrote:
> Hello all,
> This question has probably been asked on this list before, but maybe not
> quite with these circumstances. I'm hoping one of you can give me some
> direction.
> I've got a fairly typical Postfix setup... Postfix, Cyrus IMAP, ClamAV,
> SpamAssassin... all on Linux.
> Anyway, I've set up greylisting with Postgrey to help cut down on the
> junk mail that I get. I've set it up with default values (deferral of
> 300 seconds, etc). Well all seems good and fair except some of my
> regular senders can't seem to get their email through. I've checked my
> server logs and I don't even see their email address mentioned (it
> doesn't appear to even reach my machine). Several of the emails in
> question are Yahoo or Gmail. What's odd is that I have both a Yahoo
> account and a Gmail account, and I can send myself mail with no problems.
> I disabled Postgrey temporarily and had these senders re-send test
> messages from their addresses, and it worked (I got their messages). So
> something was certainly hanging things up. I just wish I knew what that was.

Do you have "smtpd_delay_reject = yes" set? If so, you should be able to
see the senders' addresses in your logs even if they were greylisted.

> This got me thinking... my ISP requires that I forward all outbound
> email through their SMTP server. Because their mail server (the SMTP
> relay I'm required to relay mail to) has suddenly been added to various
> RBLs for repeated "deferrals", is it possible that my greylisting is
> what is getting them on those RBLs?

Added to RBLs for deferrals? Doesn't make sense, or I'm missing something.

> The Postgrey does cut down on the spam significantly, particularly when
> used in conjunction with SpamAssassin and RBLs like SpamCop and
> SpamHaus. I'd like to keep Postgrey if I can, assuming that my delivery
> problems are not directly associated with Postgrey... but if my
> circumstances with my ISP won't allow me to greylist, then disabling
> Postgrey might save me a headache.
> I guess I'm looking for some advice as to whether Postgrey could cause
> problems with my ISP (they run Exim on FreeBSD and firewall outgoing tcp
> port 25 everywhere but on their one mail server) but I don't know much
> more than that), or if there are some settings I should change to
> improve my greylisting setup.

It's highly unlikely, but concentrate on one problem at a time.

When these people send to you and the messages don't make it through, do
they get a rejection or anything that might suggest that delivery failed?

If not -- while you should still be seeing their email address in the
logs -- I would guess that SpamAssassin or ClamAV snatched the message.

Now might be a good time to post your `postconf -n`.