I struggled for a week trying to setup up google mail with a custom domain to work with Outlook. I kept getting an unable to login message from the Outlook client, despite following the instructions on Google’s site (and numerous help sites) to the letter.
The issue is that there is an unmentioned setting buried in the Google account settings that no one bothers to mention. A few things contribute to this being so difficult to resolve.
1) The Outlook Message that appears has an unwieldy message in it. Something like:
"Outlook" returned the error "[WEBALERT https://accounts.google.com/ContinueSignIn?sarp=1&scc=1&plt=AKgnsbsf9BRPXiXd1yvu5M36vG9QWGxTq9VB8dFkoAw7jffOj0T64i3l-fHE4UmGycJhTpODUjDkK8SxX7Qamz0McnzZOuIsq0HPZGNIJab1cSSuvK0Ord49yXumEMy_NEpd1LQe57KKPrl9DOhZ0h1YKZgAJ67ESaH15WP3DlWsSgsV3dXjlrVgR3xDRUrL1xRlXlgQr0vkBokv_dTXQzVY8UXL_qtDMw] Web login required.." Your username/password or security settings may be incorrect. Would you like to try re-entering your password?
2) This link isn’t selectable in the error window and isn’t clickable. You’ll need to copy and paste the URL into a new browser window. Doing so will redirect you to: https://myaccount.google.com/security#signin
3) Make sure you’re logged into the Google account you want to work with.
5) Now go back to Outlook, enter your password when prompted and you’ll be able to link the accounts.
I’d love to heard from others if this is an issue they’ve had or if I’ve overlooked something. But, it took me ages to sort this out.