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

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> 1. Courier gets some 4xx error. There are other MXs available but
> as far as I can Courier tries the same MX several times if not all
> the time so message delivery is unnecessarily delayed or delivery
> even fails. Wouldn't it be better to try other MXs (same or
> different weights) in a round robin or similar fashion in every
> delivery attempt (obviously respecting weight precedence)?

4xx means "I'm busy right now, but you've reached a valid server, try
later". Why should courier ever consider a different MX? Clearly the
MX is valid and working, and if you just keep trying other ones you
look like a spam bot. Email isn't a time-constrained transport. The
message will most probably get to the destination within 4 days or
so, depending on queue timeouts, it's not urgent.

> 2. Courier's connection to the other server times out so it
> defferes message delivery. There are other MXs available but as far
> as I can Courier tries the same MX several times if not all the
> time so message delivery is unnecessarily delayed or delivery even
> fails. Wouldn't it be better to try other MXs (same or different
> weights) in a round robin or similar fashion in every delivery
> attempt (obviously respecting weight precedence)?

Courier picks a random MX, check the source if you're concerned.
Computers don't often have true random number generation, so it may
look non-random. There will be a delay between each attempt,
otherwise you look like a spam bot.

> Because the problem I see is that Courier isn't behaving as
> robustly as it could in face of difficult situations real life
> presents to a MTA. I repeat I'm not claiming Courier has a bug. I
> claiming it could have a more robust behaviour. And to be entirely
> clear, I not saying Courier isn't robust, I'm saying it could be
> even more robust.

You're the only one with this issue that I've heard of.

> If there is any further info that helps clarify my issue please let
> me know so I will provide it.

What happens when you use a manual connection, eg telnet, to do the
same message sending? SMTP has a 30 second timeout iirc. See what
happens. Use ethereal to see what's actually happening. Timeouts
generally mean the other server has stopped responding or packets
just aren't getting there. Since the other side say you're the only
one with problems it does sound like a networking issue. Where is
your server located? How is it connected to the internet? Are there
any firewalls between it and the internet? The other side is using
Postfix, I don't know of any issues with Postfix.
--
Phillip Hutchings
phillip.hutchings@sitharus.com



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