How do I access “gmail” umbrella account with non-gmail domain name?

Question

I need to search through all of someone's emails for a compliance exercise. The individual has one gmail account that he forwards all of his other accounts to. However, I get an authentication error when I try to access the umbrella account, despite the fact that I can login to the umbrella account through the browser. See specific questions after description.

This fails - note the domain name isn't gmail.com - it's user@usersfullname.com but I access it via the browser by logging into gmail.com

import imaplib
mail = imaplib.IMAP4_SSL('imap.gmail.com')
mail.login(user@usersname.com, password)

I get an authentication error ("Invalid credentials (Failure) despite the fact that the same credentials let me login on the browser. I unlocked the account etc. using these instructions: https://om4.com.au/google-apps-gmail-invalid-credentials-unlock-captcha/

I CAN login to one of the accounts that's being forwarded to the umbrella account which DOES have an @gmail.com domain name with exactly the same credentials ie:

mail = imaplib.IMAP4_SSL('imap.gmail.com')
mail.login(user@gmail.com, same_password_as_above)

Questions:

(1) Is it possible that the reason I'm getting an authentication failure that I'm using the wrong imap information - the login to the gmail account is @username.com, not gmail.com. If so, how do I figure out what the right stmp server is? It doesn't say in the Gmail Settings - Accounts & Import tab (Note: the password and username are definitely correct)

(2) Is there another reason that I could be getting an authentication error? Note that I unlocked the account - see above and my script is working for other gmail accounts...

Answer 1

Here's how I solved my problem:

Step 1) Sign in to the administrator account and follow these instructions to allow the other sub-accounts to change access to less secure apps: https://support.google.com/a/answer/6260879

Step 2) Go to specific gmail account you need to access and follow these instructions to allow access for less secure apps: https://support.google.com/accounts/answer/6010255?hl=en

Step 3) I also followed these instructions ( https://om4.com.au/google-apps-gmail-invalid-credentials-unlock-captcha/ but I'm not sure it was necessary