I have multiple clients on my computer, and monitor one client's email also, and he wants his Sage invoices, etc to go out from his email.  I just added Thunderbird to my computer, so I can keep his email separate (web mail was way too cumbersome).  So in addition to Microsoft Outlook, I have set up Mozilla Thunderbird for his email, on my computer.  I also have to send out all other invoices, etc from Microsoft Outlook.  Sage is defaulting to the new email provider - Thunderbird.  

How can I choose which email provider is used by each company,