Essentially we have multiple incoming addresses that feed into a single mailbox.  So a user can send an email to support@domain.com, tech@domain.com,techsupport@domain.com, tech.support@domain.com etc.  The issue is I can only add a single address under incoming mail lets say support@domain.com.   So if I send an email to tech@domain.com and it forwards to support@domain.com to be pulled into the system the to address is set to tech@domain.com instead of support@domain.com.  So I believe that manage engine thinks that it is a CC’d user.  So that when you click reply it adds tech@domain.com in the cc field.  So when you send an email it also sends a message to Tech@domain.com witch goes back to support@domain.com and gets added into the thread of the support request.  This can also cause a mail loop if you have notify CC users when an item is updated checked.