I used to be able to use any of my logins for my email domain/provider for sending outgoing emails. Now the account email used to authenticate the smtp client has to match the "from" for the emails. For the six email accounts that I currently am managing in Thunderbird, that means I have to go in to my account settings and change/verify a different outgoing email account every time I try to send an email message. You need to change it so in each account setting, you can specify which smtp setting is used for that email account, instead of having smtp set up as a single, separate entity.