Re: [exim] sending to only one domain per connection

On 27 Jun 2012, at 14:29, Dennis Davis wrote:
> On Tue, 26 Jun 2012, Marius Stan wrote:
>
>> From: Marius Stan <mstan@???>
>> To: exim-users@???
>> Date: Tue, 26 Jun 2012 13:59:28
>> Subject: [exim] sending to only one domain per connection
>>
>> I guess you're already aware of the new limits imposed by
>> google-hosted mail servers:
>> "Multiple destination domains per transaction is unsupported"
>
> Nope, not seen this before.
>
>> This caused a LOT of bounces lately and I still haven't figured
>> out what to do…

Well, they're 4xx errors, so unless you're sending messages to an awful lot of Google hosted domains, then you should look at your retry rules. Retry more frequently for better success.

>>
>> Any ideas on some transport/driver magic ?
>
> What do they mean by "transaction"?

Well, they certainly mean per message, which is reasonable. I see messages where ASPMX.L.GOOGLE
.COM has accepted the message for a recipient in one domain, then deferred for a different domain. I presume that this is so that they can have different content filtering policies for different domains.

That's a variation on a problem that we've discussed on this list in the past: how to allow different filtering per recipient, while still rejecting at SMTP time and not later.

The best solution with SMTP is to have filtering classes, and defer recipients when they have a different filtering class than the first recipient. Too many classes, and the message gets deferred too many times.

I don't remember discussing this in the context of a system hosting multiple domains, but it seems like a reasonable middle ground, to allow different domains administrators to have different filtering rules.


> I've never tried this, but will setting:
>
> multi_domain = false
>
> on the appropriate smtp transport do what you want?

That looks like it might be useful. It should get these messages delivered faster.

> You may also need:
>
> connection_max_messages = 1
>
> if they're restricting a transaction to a single message per TCP/IP
> connection.

Well, I think it's one recipient domain per SMTP session. I do see messages where the first Google hosted recipient is deferred. That seems over the top to me, but it might throw some spammers off track.

I'm not sure how Exim goes about gathering multiple messages for delivery through one SMTP session, but I'd experiment with multi_domain = false, and see how it goes. If you still see defers, then try this, too.

>
> ...all sounds a bit primitive to me. Perhaps they should be using
> exim as their smtp server...


Maybe they are, but it wouldn't help if they're doing what I think they're doing, for the reasons that I think they're doing it!

What would be nice would be an SMTP option to switch to LMTP. Then every recipient could have a different rule set.
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Ian Eiloart
Postmaster, University of Sussex
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