AOL says: By default, we block access to AOL Mail from outdated apps that could leave your account vulnerable. By 'outdated' they mean still using Authentication Method = Normal Password. So entering the normal password will get a block. Thunderbird is not an outdated app because it offers 'Authentication Method 'OAuth2' for AOL servers. Are you using *.verizon.net servers or *.aol.com servers? For all aol.com servers, the 'authentication method' should be OAuth2 for both incoming and outgoing. You will be prompted to verify you really are you to allow thunderbird access, so make sure cookies are enabled in Thunderbird before creating the account. * Select 'Menu app icon' > 'Preferences' * In 'Preferences' left Pane select 'Privacy & Security' * Select checkbox 'Accept cookies from sites' For verizon.net servers, use 'normal password' authentication, but when prompted you need to enter a special generated app password into TB instead of the account password. Note: imap.aol.com servers should also work using Authentication method 'Normal Password' but you will need to use 2 step and generate an app password which you use in Thunderbird instead of the normal password. Info on generating app password. https://help.aol.co.uk/articles/allow-apps-that-use-less-secure-sign-in? https://help.aol.co.uk/articles/Create-and-manage-app-password https://help.aol.com/articles/how-do-i-set-up-other-email-applications-to-send-and-receive-my-verizon-net-mail?