The other two answers are correct, but are alternatives:
- if your google account is configured to use 2-step verification you must use an AppPaswword. In this case you cannot enable less secure apps.
- if your google account is not configured to use 2-step verification, you must enable less secure apps, and log to your account from a browser in the machine where youtrack is installed (as pointed out in the comment). In this case you cannot create App Passwords.
Additional notes:
- as you can see, the youtrack configuration is the same in both cases, save for the password, which is the AppPassword if you use the first option, or the account password, if you use the second one.
- in the
from email
, the email account is ignored, but you can specify a friendly name if you use this syntax: "Friendly Name
" When someone receives a notification he'll see From: Friendly Name
. The account, whichever you specify, will be replaced by the google account you're configuring.