When you use Gmail as your SMTP service provider in 1and1Mail Account Manager, the account testing may fail. It is usually caused by 2 reasons:

  1. Gmail imposes high security standards. Google may block sign in attempts from some desktop email clients or mobile apps.

    1and1Mail Account Testing Failed - Gmail log in web browser and try again

    To use Gmail in 1and1Mail, please log in your Gmail via your web browser and go to "Less secure apps" page to turn on "Access for less secure apps".

    Turn on Access for less secure apps in Gmail
     

  2. If your Gmail account has 2-Step Verification enabled, you have to create an application-specific password for 1and1Mail.

    1and1Mail Account Testing Failed - Gmail requires application specific password

    Please visit this webpage for the instructions.

    Generate gmail application-specific password

    After you generate the app password, go to 1and1Mail and replace your original Gmail password with the 16-character password.

    Gmail 16-character app password