Many Cloud instances have experienced problems with Incoming Email Servers/Handlers recently.

Some JIRA Cloud instances are having a problem where the following error message appears in Mail Handler, preventing issues/comments creation via email:

Summary:
1 message read from the server.
Found 1 unprocessed message(s) in the pop3s folder.
Potential mail loop detected. Message will be removed.
Deleting Message 'Re: Atlassian test'

There doesn't seem to be any reason for email loops, are the email used in Incoming Mail Servers are not the same for users or notifications.

It seems that the users having this problem had emails aliases. These seem to be the culprit.

Workaround
White list the domains used by the email address with this problem

• Go to the Incoming Mail page
• Find the 'Advanced Configuration' section
• In 'Whitelisted domains' add a comma-separated list of the domains used by the emails
• Click 'Save'.