hello Tyler!It seems like Thunderbird is applying the same SMTP server settings to both accounts, which is why the username for one account is overwriting the other. This issue can happen if both accounts are using the same SMTP server configuration, and Thunderbird assumes they're sharing the same settings.

To resolve this and keep each account's SMTP username intact, here’s what you can do: 1. Create Separate SMTP Server Entries for Each Account: Thunderbird allows you to have different SMTP server settings for each account. Follow these steps to ensure that each email account has its own SMTP server configuration: Open Thunderbird and go to Menu > Account Settings.

   On the left side, under Account Settings, select Outgoing Server (SMTP).
   You'll see a list of SMTP servers. It’s likely that both email accounts are using the same SMTP server. To create separate entries:
       Click Add... to create a new SMTP server for your second account.
       Enter the SMTP server details (server address, port, authentication method) for the second account.
       Make sure to enter the correct username for this account.
   Once the new SMTP server entry is added, select it for the second account by clicking OK.

Now each email account will have its own SMTP configuration, preventing the usernames from overriding each other. 2. Assign the Correct SMTP Server to Each Account: After creating separate SMTP entries for each account, you need to make sure that each account uses the right one:

In Account Settings, select the first email account.

   Under the Outgoing Server (SMTP) section, make sure that the correct SMTP server is selected for this account.
   Repeat for the second account, ensuring that the second SMTP server (which you created) is selected.

3. Passwords and Password Manager Settings:

As for not saving the passwords, Thunderbird has a password manager to store login credentials for both incoming (IMAP/POP) and outgoing (SMTP) mail. If you don’t want Thunderbird to save the passwords automatically, you can disable this option:

   Go to Menu > Options/Preferences > Privacy & Security.
   Scroll down to the Logins and Passwords section.
   Uncheck Remember passwords for sites.
   If you don't want Thunderbird to prompt for a password every time, you could manually enter it when needed, but this setting will prevent it from saving passwords.

4. Testing the Setup:

After you've separated the SMTP servers and assigned them to the appropriate accounts:

   Send a test email from each account to verify that the correct username is being used for SMTP and that both accounts can send emails independently.
   Check the Sent folder in both accounts to confirm the proper outgoing configuration.

By following these steps, Thunderbird will correctly handle separate SMTP settings for each account, and the usernames should no longer interfere with each other.

Let me know if you run into any further issues!

This problem is caused by Thunderbird reusing existing outgoing server settings that may already exist for the same server (but different username) when setting up a new account. Thunderbird doesn't tell you those settings are being shared across multiple accounts nor gives you the option to create new separate outgoing server settings specific to the new account during the account setup process, and hence you end up changing the outgoing server settings for all the accounts sharing those settings every time you change the settings for one of the accounts…

You may create and manage multiple outgoing server settings for the same server, but cannot do it from within the main account settings. You have to do that from a separate Outgoing Server (SMTP) Settings pane you may open by selecting the corresponding option at the bottom of the list of accounts in Account Settings. The following article has a screenshot that shows the SMTP settings pane:

https://support.mozilla.org/kb/cannot-send-messages

You can add there as many settings for the same outgoing server as you want, with each entry having its own username, and then assign the right outgoing server settings to each account in the main account settings.