Why is my E-mail not downloading on my MacBook Air?

Sorry, but that is just not enough information in order for us to be able to assist you with a potential solution.

• Writing an effective Apple Support Communities question - Apple Support Communities

For example:

• What eMail client are you using: Apple Mail, Web browser, etc.?
• What eMail account are you having issues downloading emails from?
• Are you getting any error messages?
• Login to the eMail account issues?
• What have you tried, so far yourself, to resolve this so that we don't offer potential solutions that may not have already worked for you?

Ok, thanks for the additional information.

If you try accessing your ATT email from a web browser, can you do so successfully?

If so, let's try with the Apple Mail app. To start, let's verify that you have your AT&T email account set up properly. To do so, please take a look at this Apple website: Mail Settings Lookup - Apple Support

You just need to enter your AT&T email address and it should provide you with the correct email server information that will be needed by the Apple Mail app. You would use this information to verify that the proper settings are being used in the app.

Since this issue is with receiving mail, you want to pay particular attention to the AT&T's "incoming" mail server settings. (Note that there are two types of "incoming" servers: IMAP or POP3. The former is more common today and what I would expect for AT&T)

The following is an example of a fictitious Jane Doe AT&T Email account:

Ref: Add email accounts in Mail on Mac - Apple Support