With #netjunky mail_server module Odoo mass mailing server can be different from default Odoo mail server.
This kind of functionality allows you to setup one mail server for everyday use and the other for mass mailing.
If document model is mail.mass_mailing.contact email is sent through mass mailing server.
You can use for example mandrill (first 12,000 emails per month are always free) or other transactional email service for mass mailing.
Usage of mail_server module is very simple.
1) Make sure to check the technical features box for administrator user.
You can use #netjunky module company_setup for initial company setup.
This module will check the technical features box for administrator user automatically during installation.
2) Download and install mail_server module
3) Add new mail server for mass mailing or change existing.
Settings/Email/Outgoing Mail Servers