Until recently, everything worked well - comments were created via email. Now this has stopped working. In Administration > System > Incoming Mail configured mail handler "Add a comment with the entire email body". In the log file "atlassian-jira-incoming-mail.log" errors:
"ERROR [org.com] Caesium-1-4 anonymous EmailHandlers EmailHandlers[10001]: Could not find a corresponding issue to comment and 'Create a new issue from each email' is not selected."