Incoming messages: It should be possible to select account in mail handler for creation a comment and issue and attachment so no need to set permit to any for create issue, comment, attachment even if it is recognized JIRA user or it is not Jira user maybe exception if such user is project user with sufficient permit. But real TO, CC, FROM should be presented on email entry on email tab. Possibly included to the top of comment / issue description.
JETI (unlike JIRA) falls back to the default reporter to create issues or comments from emails when the sender is a JIRA user without permission.
This means it is the mail handler in Incoming Mails where you specify the user.
TO, CC, FROM are already shown in the Email log.
If email sender is a non-user, the comment on the issue says "comment sent by <email address of the external person>".
I think the above answers your questions. If not, please explain.
So I have tested that due to fact this is not work in prior version that it is used (leads to permission violation). That did not work without giving extra permits to such people. So feature fallback to default reporter works now, so it is enough for now.