A user behavior exists where a message is received, Reply is selected, the subject is changed, and information is added to the body before sending it back to the instance.

The expectation is that this email is treated as new, even though it was created as a reply.

This causes the instance to read the watermark and treat the inbound mail as a reply. In some cases, this is not desired behavior.

1. Email the instance
2. The instance creates a record and sends a notification back
   • This notification contains a watermark
3. Click Reply
4. In order to make a new email, change the subject and body
5. Send the new mail to the instance

If the instance has a reply rule, this mail is added to the existing record. If the instance does not have a reply rule, the email is not processed as new.

This is as-designed behavior.

A reply is matched by body content, subject content, or the In-Reply-To header. The In-Reply-To is placed there by the email client when you click a Reply button.
Ref. For more information, see Criteria for matching email to inbound actions.

The affected inbound email actions need to be reworked, or the prefix properties need to be changed to try to treat replies differently.