oexel@??? said:
> - config DNS so that, if his connection is down, mail for his domain
> will arrive at my box;
ie *his* DNS needs your machine in as a lower precedence MX (ie higher
number) than his own mailhost.
> - in my exim config I have to:
> - list his domain in relay_domains
or set relay_domains_include_local_mx (this has a slight risk of
allowing other people to set you up as a backup MX as well, but I've
never seen this be a real problem and its much easier to manage if you
have multiple people you relay for).
> - define a special set of retry rules for his domain so that mail
> will
> sit here until his connection comes up instead of returning an
> error
> message;
Not really, unless your normal retry rules are very short, or you are
expecting the target machine to disappear for days at a time. The only
thing is you might want to have a shorter backoff, so that you retry
connections to him (say) every 15 minutes rather than backing off to
several hours.
> my questions are:
> - is this what is called an "MX backup"?
pretty much - there are a number of terms around for this configuration.
> - is there a 'standard' set of retry rules for this situation?
not that I have seen... I would personally probably use something like
domain * F,8h,15m;F,8d,30m;
[try every 15 minutes for 8 hours, then attempt every 30 minutes for up
to 8 days]
However there are lots of issues of resource handling, how the target
box behaves etc that will modify how you want to do this.
> - is there a way for his box to send me a request for a queue run as
> soon as its connection is re-established?
Not really - it might be possible to do something with ETRN command,
however you need to test this out...
> - is there anything more to be done? how would exim handle the
> following
> situation: a domain called domain.com has two 'MX backups' like in..
> @ IN MX 10 mail.domain.com
> @ IN MX 20 mail.friend-a.com
> @ IN MX 20 mail.friend-b.com
> if mail.domain.com is unavailable, then mail.friend-a.com has to
> know
> that it should wait for mail.domain.com to come up instead of
> sending
> messages to mail.friend-b.com thus creating a loop!
The RFCs say that you only send mail on to a host with a lower MX value
than yourself (and you try to send it to the lowest available MX host).
So you do not get a loop with equal value backups.
Nigel.
--
[ - Opinions expressed are personal and may not be shared by VData - ]
[ Nigel Metheringham Nigel.Metheringham@??? ]
[ Phone: +44 1423 850000 Fax +44 1423 858866 ]
