https://confluence.atlassian.com/display/JIRA/Creating+Issues+and+Comments+from+Email?focusedCommentId=338365075#comment-338365075

The item in bold below no longer works in Jira 5.2

Default Reporter

Specify the username of a default reporter, which will be used if the email address in the From: field of any received messages does not match the address associated with that of an existing JIRA user — for example, a JIRA username such as emailed-reporter

Note:

This option is not available if the Create Users check box is selected.
Please ensure that the user specified in this field has the Create I ssues project permission for the relevantProject (specified above) as well as the Create Comments project permission for the other relevant projects to which this mail handler should add comments.
When an issue is created and this option is specified, the email message's From: field address is appended in a brief message at the end of the issue's Description field, so that the sender can be identified.