AT&T Secure Key Setup

By default, AT&T (and most email services) now requires use of "OAuth 2.0" to access the email account from a third-party application (e.g. the email app on your smartphone).

However, apps that don't support OAuth can use an alternative called "secure mail key" (aka "application password"), which means you are creating a special password for just one specific app (e.g. a security camera app).

For example, the Reolink smartphone app does not support Oauth so you need to create an app password in your AT&T account to use with the Reolink app instead of your regular AT&T password. AT&T provides step-by-step instructions to do this.