Improve the documentation about the Jira Mail Handler (catch email address setting)

Issue Description

In our documentation about the Jira Core Mail Handler, we mention the following point related to the Catch Email Address setting:

If specified, only email messages whose To:, Cc:, Bcc: lines contain the recipient specified in this field will be processed — for example, issues@mycompany.com

The problem is that since the Bcc: header will be removed most of the time by the mail server who is sending the email to the recipients mentioned in Bcc:, it seems that there won't 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).

We have 2 open bug tickets about the fact that the Catch Email setting does not work when the email address is in Bcc::

• for JIRA Cloud: https://jira.atlassian.com/browse/JRACLOUD-44680
• for JIRA Server: https://jira.atlassian.com/browse/JRASERVER-44680

However, it is not JIRA bug, since the problem comes down to the fact that by design, mail servers will remove the Bcc: header.

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 our documentation 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