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I have had a postfix mail server up for quite a long time, running on Ubuntu Server x86_64. It is managing emails for multiple domain names. However, it has decided, seemingly arbitrarily, to stop accepting any extra-domain emails to a single domain.

If I mail a.com from a.com, it works, but the moment I mail to a.com from b.com (regardless of b.com being on the same server or not), it does not accept anything. I can't find any mention of the problem in error logs.

I have tried doing upgrades via apt-get, but the problem has not been fixed. Rebooting or restarting the service does not fix it.

According to postconf -d | grep mail_version, I'm on v2.9.6. I am using MySQL for the virtual user accounts. It is using dovecot v2.0.19.

Where should I start looking for where the problem came from? And how to prevent it from happening again?

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  • You should start at /var/log/mail.log it will log each email received and tell you what postfix did with it, does the sender at b.com get a NDR?
    – squareborg
    Apr 10, 2013 at 20:53
  • mail.log only seems to be showing what is coming through postfix/smtpd. If I switch to using that mail server for SMTP, the emails do in fact go through. But I can't have the rest of the world using my SMTP. No alert shows up in the log at all when I use any external SMTP. From Yahoo, I get a Mail server for "a.com" unreachable for too long bounce. I haven't received bounces on other mail servers I've tried... Apr 10, 2013 at 20:59
  • Ok... on further notice, mail.log DOES track when I receive emails to other domain names (like b.com). It doesn't track anything when I receive emails to the problem domain, a.com, from an external SMTP. Almost like something is taking over my MX record on the DNS level. Something to look into at least... Apr 10, 2013 at 21:02
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    Have you checked that your domain has not expired and your MX records are correct? Is port 25 accessible from the outside intrnet?
    – Grant
    Apr 10, 2013 at 21:05
  • Like Grant says your domain could have expired and your mx reset, mxtoolbox.com is a good tool to check smtp connectivity on a domain.
    – squareborg
    Apr 10, 2013 at 21:16

1 Answer 1

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Since nobody ever answered, I will answer for myself.

The problem arose because Network Solutions shut down the domain name. It appeared they had an old email address on file, hence why the owner of the domain never received any notice about their domain nearing expiration, then subsequently expiring. They then parked the domain, and the MX records were invalid at that point. Renewing the domain fixed the problem.

If anybody else gets this problem, please check that your domain names are functional and haven't expired!

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