Re: problem with mx ip selection on retries

On 2 Nov 2010, at 11:25, <[email protected]> <[email protected]> wrote:
> I found an problem in xmail when re-trying to connect to mx with multiple
> ips
> 
> Here is a sample :
> Assuming domain XX.com have this dns setup
> 
> xx.com	mx 10	mx10.xx.com
> xx.com mx 20	mx20.xx.com
> 
> mx10.xx.com	A	10.10.10.1
> mx10.xx.com	A	10.10.10.2
> mx10.xx.com	A	10.10.10.3
> 
> mx20.xx.com	A	20.20.20.1
> mx20.xx.com	A	20.20.20.2
> 
> supposing xmail have now to send a mail @xx.com
> on first try it use mx10.xx.com at 10.10.10.1 : now the tcp connection don't
> work
> then os same first try xmail use mx20 at 20.20.20.2 : suppose tcp connection
> don't work too !
> 
> What i see in a trace is that for ALL the others retries for this mail,
> xmail retries ONLY on SAME ips, 10.10.10.1 and 20.20.20.2
> It never retry on others mx's ips !! And because there was no response from
> these two ips, mail bounced back to sender after all possible retries :-/
> (i checked the others ips, they responded correctly :-/ but xmail never
> tried them ...)
> 
> I think this is a major bug :(

It's not violating the standard, but in the interests of robustness, I agree that it is a problem.  See:
http://tools.ietf.org/html/rfc5321#section-5

Another peculiar XMail behaviour is that even if the hostname in an MX record is unknown, XMail logs an error but then tries again.  This only makes sense if the recipient fixes his MX records, which I think is more likely if the mail is permanently failed rather than temporarily.  In Postfix, it's user-configurable which method is used.  Again, no violation of the spec, but my preference is for a behaviour that is somewhat more robust, especially today with spam-filled queues everywhere.

Cheers,
Sabahattin
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