Re: [Exim] Failing behviour based on SMTP codes.

> This seems the Right Thing in the case when there's only one host
> involved. It is less obvious in the case where the domain routes to two
> hosts, and the first one that is tried gives one of these 5xx codes. Do
> you try the other host? With this new code Exim does not. This is the
> same behaviour as happens with a 5xx response to MAIL FROM or RCPT TO,
> and I think it's the right thing to do, but do you agree?
>

When you say the domain routes to two hosts, do you mean that there are
equally preferenced MX records?

My thoughts on this would be that one should treat a 5xx response from a
*primary* (i.e. lowest preference number) MX as permanent, but if the
response came from one of the less preferable MX hosts, it should be treated
as if that host was unreachable. This would be useful in this example:

MX 5 mail.domain.com. (down)
MX 10 backup.otherdomain.com. (temporarily broken)
MX 15 never.broken.mail.host. (working great)

Exim would try MX 5 and find it was down. It would then try MX 10, which
gives a 5xx response to HELO. Then, it would try MX 15 and the mail would
go through.

Of course, if MX 5 is the one that gives the 5xx, there's no reason to keep
trying and the message should be sent back with a nasty note attached.

--Trevor

---
Trevor Sky Garside
trevor@???