Final answer:
To address the issue of not being able to receive external emails, it's essential to verify email server settings, email account configuration, email filters or rules, and email server connectivity.
Step-by-step explanation:
In this scenario where a client is not able to receive external emails, several checks should be performed to troubleshoot the issue. Initially, email server settings should be reviewed to ensure that the domain is correctly pointed and the server is configured to accept incoming messages. Next, email account configuration must be examined to ascertain the account exists on the server, and there aren't any misconfigurations causing the emails to bounce back. Moreover, verifying email filters or rules is crucial in case wrongly set filters are rejecting or rerouting incoming external emails. Lastly, email server connectivity should be confirmed to make sure that there is no network issue preventing emails from reaching the server.
Each of these areas provides a piece of the puzzle in resolving email issues and would need to be systematically checked to diagnose and fix the problem of not receiving external emails.