[nSLUG] postfix config and half broken domains

D G Teed donald.teed at gmail.com
Tue Nov 27 11:28:34 AST 2007


Hi all,

We have seen a problem with email handling for domains which
exist but there is either no MX registered for them, or the
DNS server cannot be reached.  Of course this story
gets more complicated by the black box of Exchange
entering the picture.

There is an example domain of chnsradio.com which will
illustrate the problem.  If I fire off an email to there from
Thunderbird directly going to postfix SMTP, it does not
enter the queue - it causes a rejection notice pop up of :

>  An error occurred while sending mail.  The mail server
>  responded: <chnsnews at chnsradio.com: Recipient
>  address rejected: Domain not found.  Please check
>  the message recipients and try again.

This result is perfect for users like me, but many of our users
are on Exchange.  Exchange server relays through the same SMTP,
but Exchange allows the Outlook clients to put the email
into the Exchange queue when the domain has no MX.
The result is a queue that goes nuts on Exchange, retrying
every minute and they have to delete mail.

Obviously, something is wrong with Exchange, but the
sysadmin of that box cannot find a solution, so he is asking
me if postfix can accept the messages into the postfix
queue regardless.  That would be done by removing
reject_unknown_recipient_domain from smtpd_recipient_restrictions
The painful part of that would be learning typo'ed email addresses
were not sent several days later.

Maybe someone else on the list has run into this problem
and knows of a better solution.  Using delay_warning_time
without reject_unknown_recipient_domain is about the best
option I can see at this point (this is purely outbound postfix instance).

This has happened a number of times for different domains, so
we'd rather not take an access list type of approach.

--Donald



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