Sometimes, there is no problem in sending emails but emails are not recieved at recievers end.
The first you should do is to check the exim mainlog using following command
tail -f /var/log/exim_mainlog
If you can see the error as below
The first thing is to check whether the domain exists under
If not then add the domain under
and remember to remove the entry from
If still you are getting same error then check the resolv.conf file in which DNS used is of same server or not. If it is of same server, and example.com is just using A record to point the domain to your server and all other records are external like MX then just delete the zone file i.e
This will fix the issue.
If any feedback, queries are always welcome!