This is something that I usually forget so I decided to post it here, probably would be helpful for someone else. If you want to configure multiple outgoing server settings in Thunderbird then you need to go to Account Settings and scroll down to find Outgoing Server (SMTP) as shown in the following screenshot.
Then you can add your new SMTP server configuration by clicking the Add button.
Afterwards you can use any of your outgoing SMTP servers when configuring a new email account. If you have multiple email accounts then you can setup each one with its own SMTP server settings.
