Microsoft Exchange 2010
NOTE: This bug report is for JIRA Server. Using JIRA Cloud? See the corresponding bug report.
Outlook uses the "References" header for threading, but JIRA only adds the "In-Reply-To" header to outgoing emails
NotificationInstance's should have a creation date, and a service to clean them up
Outgoing emails not threading in Outlook
Outgoing emails not threading in Outlook when connected to Exchange Server