I got an email pretending to be AT&T. How can I find out if I it did any damage?
Did you click on anything in it to open something or not? If not then I doubt it's done any harm as it was most likely just spam.
Run a scan with VirusScan just in case, you should be OK.
Keep your system up to date, all aspects of it, and perhaps arm your self with some extra anti-malware such as the 3rd Party Tools mentioned halfway down this page: https://community.mcafee.com/docs/DOC-2168