I'm posting this issue again because I'm desperate to get it solved!!
We have adjusted every possible setting to get our JIRA working the way it did previously and we are desperate to get it working again.
We are using the Service Cloud version of JIRA for our project.
We prefer to reply to each ticket via Outlook instead of using the JIRA comment process. We have the mail handler set to send a copy of each ticket to my personal email address. When a ticket was received, I would reply to the email, ensure the support email address and the user's email address are in the TO field and the ISSUE KEY was in the subject line and the reply would show as a comment on the JIRA ticket.
Currently, each time I reply to an email, a new ticket is created.
I hope someone will know which settings will allow the comment to be added to the ticket without creating a new ticket.
Please let me know if there are any details I have neglected to include.