A reply email with a valid in-reply-to header is detected as newIssue An email is received that is a "reply" to an email sent from the instance.The notification that sent the originating email has "Omit Watermark" checked.The subject of the reply email was edited to remove the "RE:" prefix and the case number. According to the documentation Inbound email actions (servicenow.com) it was expected that this would still classify as a reply based on the in-reply-to email header. The system classifies an email as a reply when it fails to match it to the forward receive type and it meets any one of these criteria: The subject line or email body contains a recognized watermark such as Ref:MSG0000008.There is no watermark and the Reply-To header contains a recognized message ID of an email with a target record.There is no watermark and the subject line contains a recognized reply prefix such as RE: and a recognized record number such as INC0005574CauseWhen verifying the originating "Sent" email we don't check for the target record directly but rather query for the watermark.As the sent email had no watermark we could not identify the target record and thus the email was classified as "New".ResolutionIn order to solely reply upon the in-reply-to header to classify an email as a reply the originating "Sent" email must contain a watermark.Related LinksThere is a task to clarify this in the documentation.