Our situation. 

    Odoo9 Enterprise

     10 users, Every one has their own e-mail ( User1, User2, such as ... in google business suit).

     Outgoing e-mail servers have been configured with all the 10 users's credentials with same priority, and test is passed.

All the users's communication via ERP is captured in User1's sent box in Google business application as the odoo9 sent all thermals via first user.

Is there any way  to force the odoo9 to sent via individual outgoing e-mail server?