RE: [Exim] How to treat SMTP error 550 (Relaying denied) as …

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Author: Exim Users Mailing List
To: Exim Users Mailing List
Subject: RE: [Exim] How to treat SMTP error 550 (Relaying denied) as a temporary failure
[ On Wednesday, November 22, 2000 at 16:28:44 (-0500), David Searles wrote: ]
> Subject: RE: [Exim] How to treat SMTP error 550 (Relaying denied) as a temporary failure
> While not "tied" to the ISP, we've otherwise had very good luck with them.

OK, then if they're otherwise doing good by you there's some chance that
they'll be able to fix their system and keep you as a customer! :-)

> We must use their relay because places like AOL and other huge mail
> recipients will not accept inbound SMTP from dynamically assigned IP
> addresses (like when we have exim connect directly to the recipient). In
> order to be able to send mail to everyone in the world and not have it
> bounce, we must relay thru the ISPs mailer.

Ah, yes, of course.

That's sort of what I was guessing, and why I wondered if it might not
be possible for you to switch to another ISP that would give you a
static address. You'd probably have to "upgrade" to a full-time
connection, so hopefully this is within reason for your situation.

> These 550's occur fairly rarely (once out of 750-1000 outbound mails;
> probably some timing window in their "POP before SMTP" implementation).

That's more often than I'd be willing to put up with too, I think.

> Since the failures occur so rarely, I'd like exim to automatically retry the
> message as it will almost certainly be accepted the next attempt.

There are mailers that will treat a 5xx response as if it were a
temporary error (i.e. reply-100), and perhaps Exim can be configured to
do this too. The problem is that you end up retrying truly permanent
errors for much longer than you should and that annoys both the
postmaster at the site that's trying to tell you to bounce the message,
as well as your user who's message is stuck in your queue for the
duration of the retry timeout.

It's best to stick to the protocol spec and always bounce messages
immediately if a 5xx error is returned, and instead to try and coerce
the responsible party at the other end to fix their broken mailer! ;-)

                            Greg A. Woods

+1 416 218-0098      VE3TCP      <gwoods@???>      <robohack!woods>
Planix, Inc. <woods@???>; Secrets of the Weird <woods@???>