I'm an administrator of our Jira Cloud instance and am trying to create a new mail handler to automatically create issues from an IMAP mailbox. We already have this configured for another mailbox and it's working perfectly.
If we send in an email from a registered user without any links in the mail body it processes correctly.
If we send any emails from a non-jira user's mailbox it fails (even with "Default Reporter" set). Also interestingly the grey icon next to the "Default Reporter" box has tool text saying I don't have permission to browse users (I should), but the auto complete appears to still work. The user "beccy" definitely has JIRA access and can create issues.

I can see this issue might be related to JRASERVER-30521 which is a long lived bug that doesn't appear to be being addressed.