When sending an email, you may find that the recipient did not receive the email. You will also find the email failed to send in WHM >> Mail Delivery Reports with the result:
host lookup did not complete
You will also see this error when testing mail deliverability to the recipient via SSH:
# exim -bt email@example.com
firstname.lastname@example.org cannot be resolved at this time: host lookup did not complete
This occurs when the server is unable to resolve the recipients' domain and is typically due to the nameservers that are configured in /etc/resolv.conf or WHM >> Resolver Configuration.
Use WHM >> Resolver Configuration to remove the current nameservers from /etc/resolv.conf and add new nameservers that can resolve remote domains. For example, Google public DNS servers 18.104.22.168 and 22.214.171.124.
Optionally, you can edit /etc/resolv.conf via SSH by following these steps:
1. Connect to the server via SSH as the root user.
2. Open the /etc/resolv.conf file using any command-line text editor you prefer (example: vi, vim, nano, etc.)
3. Comment out the current nameservers by adding a '#' in front of each nameserver and add the new nameserver entries:
4. Save and close the file.