AOL requires that you generate an app-specific password for use in third party apps like Aqua Mail. To generate a password you must:

  • Open your AOL account in a web browser and go to your Account options
  • Under Account Security, scroll down to select Generate app password
  • In the following windows select Other App and write the name of the app

When adding your account in Aqua Mail instead of your normal password, use the one you have just generated.

P.S. It appears that AOL has "temporarily" disabled the password generation feature, effectively requiring users to utilize their own platform. Until they resolve this issue, you will be unable to access your account in Aqua Mail.