Improve the description under the Catch Email Address setting of JIRA Mail Handlers

Issue Description

When configuring a mail handler in JIRA > ⚙ > System > Incoming Mail, we can see that following description is displayed under the Catch Email Address* field:

If set, only emails having the specified recipient in fields To, Cc or Bcc will be processed.

The problem is that since the Bcc: header will be removed most of the time by the mail server that is sending the email to the recipients mentioned in Bcc:, there might not be any scenario or use case where the mail handler will actually catch the email address from the Bcc: (since it might never be there).

The only scenario where the Bcc: won't be removed (tested in gmail) is when the email address in the From: and in the To: headers are the same: in this case, the email received by the sender (who is the same as the recipient) will still contain the Bcc: header. But this use case does not seem to be a scenario that will be used by our customers, since most of the time the email in the From: and in the To: headers will be different.

Suggested solution

Improve the description of the Catch Email Address setting by mentioning that:

• the JIRA Mail Handler will catch the email address in the BCC: header only if it's there
• since the mail server will likely remove the Bcc: header, therefore we don't recommend adding the catch email address to the BCC: header, but to the To: and Cc: header instead