Note: AT&T uses the Yahoo Mail servers to provide its customers with webmail services. The instructions below show you how to add an email signature to your AT&T email account.
Once you are ready to set up your email signature, log in to your AT&T account using a web browser. At the top right, click the settings icon and select Settings.
In the left column, select Accounts. On the right side you will then need to select your email account.
Scroll down until you get to the Signature section, then paste your new signature into the text box provided and ensure that the “Append a signature to the emails you send” box is ticked.
Click the Save button and click to compose a new email message. Enjoy your new signature!