You very often see this kind of behavior. The email is send from a noreply@domain.com and then there is a Reply-To: in the header or there is a reply email address (mailto) in the message body where a user can click on to reply on the email.
To make things more complex 
Mostly the Reply-To: is an email alias. So when a company sends an invoice by email, the From: will be noreply@domain.com, the Reply-To: will be e.g. invoice@domain.com. So multiple users gets your reply in their mailboxes. Maybe in Tryton this email addresses can be added on groups? So users who are in that group can fill the Reply-To: also with that email address.