Thanks a lot ntozier. However that's not exactly the workflow described in my opening topic. I'm going to put it shorter in this post:1.- CUSTOMER sends an email to STAFF1 (someone at my company) asking for support.2.- STAFF doesn't know how to help CUSTOMER, so he replies the email (from Thunderbird or Outlook) adding SUPPORT email (the email address used for piping in my osTicket installation). He wants to be aware of the issue evolution, so he'll own the ticket.3.- A ticket is created, with STAFF1 as the owner and CUSTOMER as a collaborator. That works like a charm :)4.- The osTicket administrator assigns the ticket to STAFF2 (a technician who knows exactly what to tell to CUSTOMER).5.- STAFF2 replies from osTicket.6.- (This is what's working wrong, in my opinion): STAFF1 receives an email notificacion, but CUSTOMER (the collaborator) doesn't.I can't check my mail server right now, but I'll do first time monday morning :) Thanks a lot for your time again!