Configure Origin Address for Multiple Gmail Accounts
Thunderbird can be used to manage multiple email accounts. These accounts can either be from the same or different email providers. However, when you have multiple Gmail accounts, by default Gmail will use your default account as the "From" and "Reply To" addresses. You must manually configure an alternate email address to be used as the "From" and "Reply To" values in messages.
Load Gmail in a browser window and click Settings in the top right corner.
Select Accounts and Import.
In the "Send mail as" section of the page, click edit info to the right of the desired account.
Click "Specify a different "reply-to" address" and specify the address you want to use as the "From" and "Reply To" address in messages.