Troubleshooting an Email Box Service

Make sure that your DNS is configured correctly for the domain in question. See KBA: Email Box Service DNS defaults
Verify your user name and password via the webmail login. See KBA: How to Access an Email Box Service Webmail
In the webmail, look for messages that indicate you may be over the service limits. See KBA: Email Box Service limits
Attempt to send an email to this email account from this email account and verify that it received. Note any failures
Attempt to send an email to a Gmail account. Note any failures or bounce messages.
Send an email from a Gmail account. Note any failures or bounce messages.
Attempt to resend the message you originally sent, verifying that the email address and domain is correct
Have the sender resend the message originally sent to you, and have them verify your email address and the domain is correct
Have the sender send any bounce messages to you through an alternate method

If all else fails, open a support ticket on the help desk and paste the messages received.