Code:
Mailserver-Domain: smtp.gmail.com
Mailserver-Port: 25
My name: display name in mail
Meine Email-Adresse: <username>@gmail.com
Benutzername: <username>@gmail.com
Passwort: same as Gmail webpage password
Notes

* "less secure apps" must be allowed
* additionally after activation the following Gmail-page for unlocking must be visited https://accounts.google.com/b/0/DisplayUnlockCaptcha
* for more information visit this help page https://support.google.com/mail/answer/7126229?hl=en
and read "I can't sign in to my email client"