There can be hundreds of reasons that an email you were expecting did not arrive, but the vast majority of cases are very similar. Some initial trouble shooting can greatly assist in finding where the problem lies.
Steps to follow:
- Check that the senders domain is not on a RBL (registered black list) for spam.
Go to http://mxtoolbox.com/blacklists.aspx and enter the senders domain name e.g. enter domain.com if email is coming from firstname.lastname@example.org
The sender will receive a bounce back message with instructions on how to request a review of their domain.
- Make sure that your mailbox has not exceeded its quota
Review this under 'email accounts' in cPanel
- Make sure that your MX records are correct
Each MX record points to an email server that’s configured to process mail for that domain. In most cases this will be the server your site is hosted on, unless you have your mail hosted elsewhere.
Review this under 'MX Entry' in cPanel