When user A sends email M1 from task T1 to user B: Celoxis system stores the email in it's database, changes the reply to

celoxis+<control information>@company.com

and sends it to user B. When user B replies, the email lands up for the celoxis inbox (not user A's inbox) Celoxis periodically polls the inbox and when it finds the reply emails there, processes it by first looking at the control-information. The control information has the task and original message id encoded in it. After the replied email is filed, celoxis sends the email to user A (again with the reply-to header changed to

celoxis+<control-info>@company.com