Multiple SMTP servers - Thunderbird
From MozillaZine Knowledge Base
You can set up Thunderbird to use more than one SMTP (outgoing) server, or to use the same server with different usernames and passwords, so that each of your mail identities can have its own SMTP server configuration.
To add an additional SMTP server:
To use this newly added SMTP server for an account's default identity:
To use this newly added SMTP server for any other identity:
Note: When you press the Manage Identities... button and change settings there for the default identity, bug 373573 can prevent the Outgoing Server (SMTP) setting from transferring back to the main Account Settings page. To work around this, use the main Account Settings page to change this setting.
If you have set up multiple SMTP servers and periodically need to change the default SMTP server (perhaps you have a laptop computer that you use on different networks depending upon whether you're at home or work), you could add a button to the toolbar to select the SMTP server using the SmtpSelect extension or the Buttons! extension. You need to right click on the toolbar, drag and drop the button to the toolbar, and then press the OK button to do this.
If you have set up a new SMTP server, associated it with one or more of your mail identities, and find that you cannot send mail with it, try going through the points listed on this page.