Re: [courier-users] Re: Automatically use secondary MX host if primary

Rodrigo Severo wrote:

> Ben Kennedy wrote:
>
>> Maybe on a 4xx it would make sense. I can't see how it would with a
>> 5xx,
>> though. If you have 2 MXs and they don't agree on who is a valid user
>> (for example), you have bigger problems.
>>
>>
> My fault. You are right. There is no good reason to try a second MX if
> I get a 5xx error.
>
> There still remains the 4xx error situation and the "Connection timed
> out" => "deferred" situation. Why not try a second MX in these
> situations?
>
>> If it's "turned off", then Courier would try and fail and move on to the
>> next one, as it currently does, so what's the difference?
>>
> Yes you are right again. I mentioned this because I had this problem
> with a very old Courier version I was running some time ago. Old
> problem already solved.
>
> But again ther still remains the server too busy situation where I end
> getting a "Connection time out". Wouldn't it be good to try a second
> MX here?

It's my understanding that Courier would defer the message for awhile
after the 4xx (which is exactly what a 4xx error is asking it to do) and
then re-evaluate the MX records. So if there were two mx records of the
same weight, it would eventually try the 2nd one. In other words, I
don't believe Courier "caches" the DNS lookup between attempts but I
could easily be wrong on this. Sam?

Also, I believe a heavy load server should be configured to refuse
connections when load is high rather than accept only to defer with 4xx
errors due to overtaxed resources. Courier does this per the MAXDAEMONS
and MAXPERIP settings. If your pushing your system resources and
running into timeouts, this number should be lowered. If the connection
is refused rather than deferred, then a well behaved server will then
try the next MX record.

Jay

--
Jay Lee
Network / Systems Administrator
Information Technology Dept.
Philadelphia Biblical University
--



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