[Lula] Mail server ip changed issue.

[Jeff Carlson]

Alan Ptak wrote:
> I'm also a firm believer in secondary DNS and backup MX services on 
> different networks for availability purposes, and use both as standard 
> practice. For under $50/year, it's cheap insurance.

I've seen this debate before.  In the end, I decided that a secondary MX 
wasn't really worth the trouble it causes.  Every plus it provides seems 
to be negated by something else.

First of all, properly configured mail servers queue.  I think most 
servers are set by default to five days.  If the message isn't delivered 
by then, it bounces back to the sender.  If the message is picked up by 
a secondary MX, but doesn't make it to the final destination, there's a 
greater possibility of the bounce not making it back to the sender.  Not 
that a secondary is somehow less reliable, but it's a longer path back 
to the origin, and we are talking about a situation where something has 
gone wrong already.

Second, I have seen secondary MXes used to circumvent filtering.  Since 
the secondary would logically be white listed, spammers sometimes send 
directly to the secondary to avoid filtering in place on the primary. 
This is even more of a problem if you don't control the secondary, as 
you are proposing here.

Third, if you do control the secondary, then it's another box exposed to 
the Internet that you have to worry about.  Spammers will try to relay 
through it, you'll need to keep it updated, etc.  Sure you would take 
care of it anyway, but it's another consumer of your resources.  Do you 
need that?

Email was originally designed with the idea that its delivery was 
unreliable.  Queuing is part of the equation for this reason.  Sure, so 
is a secondary MX.  This is just the view I have taken on the situation.
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