Complex IMAP and SMTP email setup
Internet service providers like AT&T provide gateways handling direct email sending using SMTP. However, due to the real hazard of enabling bad actors to abuse mail gateways to send unwanted spam abroad, there are some extra steps needed to help hold users accountable.
Large consumer email providers like Google, Microsoft, and Apple typically have presets already in place in most email clients to make setting up email access easy, just provide your username and password.
If you have a vanity or custom email service, you will need to carefully configure settings to allow custom email from address. For AT&T this is done through a special settings portion of their webmail application.
Email clients like what Apple iPhones provide for iOS will need to use a special cryptographic key for the SMTP outbound email gateway. For AT&T these keys are managed online by customers, just look for the special links when logging into manage and set up payment for Internet access. Take special care to copy the key immediately, as it will be displayed only once when created.