Sporadic "Unrouteable address" error message

[albatroz]

Several of my customers are reporting sporadic problems receiving email messages, so after running grep over the /var/log/exim_mainlog file, I found several lines like these:

2015-10-21 17:10:19 1Zp1Cc-0002RY-Hq ** [email protected]: Unrouteable address
2015-10-21 17:10:19 1Zp1Cc-0002RY-Hq ** [email protected]: Unrouteable address
2015-10-21 17:10:19 1Zp1Cc-0002RY-Hq ** [email protected]: Unrouteable address
2015-10-21 17:10:19 1Zp1aN-0006DO-50 ** [email protected]: Unrouteable address


The problem is that some of those email addresses really do exist.
So my question is, what is causing this issue?

 

[dalem]

1. your DNS resolvers on the sending are not set up or working correctly
2. The DNS on these domains are not set up or working correctly

 

[cPanelMichael]

Hello

Check to ensure you are using working resolvers in your /etc/resolv.conf file. Also, ensure the domain name is added to the /etc/localdomains file if it's email is handled by the local cPanel server.

Thank you.