If you have problems with your cPanel server not receiving mail from certain email addresses here is why:
When cPANEL in in the process of receiving a message, it contacts the sender’s server to establish a verification connection.
If the connection times out or the sender’s server is configured in such a way that it rejects the connection, the result is: Sender verify failed
In my case the sending server is running ISPConfig, that hosts a site with a email web form.
To resolve this, you need to add the recipient server IP in WHM Home -> Service Configuration -> Exim Configuration Manager -> Sender verification bypass IP addresses.