Email setting
I have 2 different yahoo email accounts that I access through Thunderbird. When I added the 2nd account, it changed the SMTP Server Settings "user name" of the 1st one to the same as the new one. I received an error when I tried to send an email from the 1st account, after looking at the settings, i noticed the SMTP user name was wrong. When I changed it on the 1st account, it automatically changed it on the 2nd account as well.
Opaite Mbohovái (1)
Make separate smtp servers for each account, with identical settings except for the User Name (email address), and give them distinct Descriptions. Then, set each account to send on the smtp that has a matching User Name.