Email Relay Issue with Remote MX Domains
Hello,
We’re experiencing a problem with email delivery on one hosting and would appreciate any insights. Here are the specifics for reference:
Setup Overview:
- Primary Domain (example.com): Uses a local mail server, and email routing is set to Local Mail Exchanger.
- Addon Domains (example2.com and example3.com): These domains host only websites on our server, while their MX and rest of DNS records are managed externally. Email routing is set to Remote Mail Exchanger.
Issue Summary:
- Emails from example.com to example2.com are successfully delivered.
- Emails from example.com to example3.com fail with an SMTP relay error.
Successful Delivery Log (example.com to example2.com):
2024-12-04 13:55:05 cwd=/var/spool/exim 3 args: /usr/sbin/exim -Mc [ID-MASKED]
2024-12-04 13:55:05 <= sender@example.com U=mailnull P=spam-scanner S=60779 id=[MESSAGE-ID-MASKED]
2024-12-04 13:55:12 => recipient@example2.com R=dkim_lookuphost T=dkim_remote_smtp H=mail.example2.com [IP-MASKED]
2024-12-04 13:55:12 Completed
Failed Delivery Log (example.com to example3.com):
2024-12-04 13:46:50 cwd=/var/spool/exim 3 args: /usr/sbin/exim -Mc [ID-MASKED]
2024-12-04 13:46:50 <= sender@example.com U=mailnull P=spam-scanner S=1376 id=[MESSAGE-ID-MASKED]
2024-12-04 13:46:51 ** recipient@example3.com R=dkim_lookuphost T=dkim_remote_smtp H=mail.example3.com [IP-MASKED]
SMTP error:
550-Please turn on SMTP Authentication in your mail client or login to the IMAP/POP3 server before sending.
550-[LOCAL IP ADDRESS]:40920 is not permitted to relay through this server without authentication.
Key Points:
- Test emails are sent through Roundcube Webmail and the mentioned error appears immediately after clicking "Send."
- Email Routing and DNS settings have been verified multiple times.
- The manualmx file is empty.
- Interestingly, email delivery to domain2.com (also using a remote MX server) works, while emails to domain3.com do not.
Could there be a specific configuration or relay issue affecting domain3.com? Any insights or suggestions would be greatly appreciated.
Thank you in advance for your help.
Michel
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Hey there! It's odd that domain2 would work when domain3 doesn't. However, that error that you posted does give us some things we can check.
Could domain3 be listed in /etc/localdomains even the the mail routing is set to remote?
That is the only option in the mail configuration that would be unique to domain3 and not domain2, so I'd start there.
You're also welcome to create a ticket so this can be investigated directly.
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Hey,
Thanks for your suggestion!
We’ve checked both
/etc/localdomainsand/etc/remotedomainsto see if domain3 might be listed incorrectly. Below are the results from our investigation:[root@server ~]# egrep example3.com /etc/{remote,local}domains
/etc/remotedomains:example3.com.example.com
/etc/remotedomains:example3.com
[root@server ~]# egrep example.com /etc/{remote,local}domains
/etc/remotedomains:example3.com.example.com
/etc/localdomains:example2.com.example.com
/etc/localdomains:admin.example.com
/etc/localdomains:example.com
[root@server ~]# egrep example2.com /etc/{remote,local}domains
/etc/remotedomains:example2.com
/etc/localdomains:example2.com.example.comIt seems everything is configured as expected, with domain3 listed only in
/etc/remotedomains. This issue is quite puzzling since email routing andmanualmxusually address such problems. However, domain3 is still not functioning as intended, even though domain2 works without any issues.We’d appreciate any additional insights you might have.
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I'm not sure what else could be causing this behavior. It would likely be best to create a ticket so this issue can be investigated directly on the server.
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