In some cases we may be unable to receive e-mails from another e-mail accounts. If you are pretty sure that there is no issues with the mail relaying settings in the sender and receiver end, then it might be due to the SpamExperts option enabled in the receiver end. You can check the logs from the receiver end and it will shows the reason for which the receiver end was denying mails from the sender.
♦ Login to cPanel (https://example.com/cpanel)
♦ Go to Mail >> SpamExperts >> and login to the corresponding domain.
♦ Provide the sender and receiver e-mail accounts in the corresponding fields and the go for the log search.
This will shows the reason for denying mails from the sender e-mail address.