Greetings.
We would first recommend confirming whether or not the emails have made it to your server as a whole. You could do this using the "exigrep" utility, which we have some information on here:
If you're having trouble sending or receiving e-mail, you can find out what the problem is using exigrep. Exigrep is a Perl script that allows you to search for a string in the exim logs and re...
support.cpanel.net
If the messages have not reached the server as you mentioned, then we would recommend speaking with the manager of the external email host to see if there is any issue with transport from that end.
If the messages are received to your server and do not appear in the email accounts, then we would recommend confirming whether or not there are any mail clients that are connected to your destination address. You can review this using the information here:
Question How can I see who is logged into my email server? Answer Dovecot includes doveadm which can search for currently active users with the 'who' option. For more information, please read the ...
support.cpanel.net