Alias setup in Thunderbird

• Access Tools -> Account Settings
• Select the mailbox to which the alias will be delivered by clicking on the top-level for that account's settings
• Click the Manage Identities button on the bottom right of the window
• A new window will open. Click Add
• At the very least, complete the following settings

Your Name: The name you wish recipients to see
Email Address: The email address of the alias
Outgoing Server (SMTP): This must match the SMTP server for your mailbox