The Epic Name field is a mandatory field when creating Epic Issue Types.
However, if the user selects the Epic issue type to be the default issue type for a mail handler, JIRA won't complain about the Epic Name being blank.

Steps to reproduce

1. Setup a mail handler with the Epic issue type selected;
2. Send a test email to this mail handler

Expected
JIRA would not create any issues from emails arriving the mail box because it's not possible to set the Epic Name in the mail handler.

Actual
A JIRA issue is created just fine using the message body and subject.