This requires admin access, Google credentials

OAuth setup

1. Follow OAuth 2 Google service to get the Client Id and Client secret.
2. Enable Gmail API in the Google Developer console.
3. Login as admin.
4. Navigate to Site Administrator > Server >  OAuth 2 services
5. Create a new Google service called: Gmail - OAUTH2.
6. Set the Client id and Client secret.
7. Set the Scopes included in a login request value to: "openid profile email https://mail.google.com" (Without the quote).
8. Set the Scopes included in a login request for offline access value to: "openid profile email https://mail.google.com" (Without the quote).
9. Save changes.
10. Click Connect to a system account and finish it.

Initial setup - SMTP

1. Navigate to Site Administrator > Server > Email > Outgoing Mail Configuration.
2. Set the following value:
   • SMTP hosts: smtp.gmail.com:587
   • SMTP Security: TLS
   • SMTP Auth Type: XOAUTH2
   • OAuth 2 Service: Gmail - OAUTH2
   • SMTP username: The username that was used to connect to Google Developer Console.
3. Save changes

Outgoing mail testing

1. Navigate to Site Administrator > Server > Email > Outgoing Mail Configuration -> Test outgoing mail configuration
2. To email address: Your email address to receive the test email.
3. Additional subject: Test email using XOAUTH2
4. Press Send a test message.
5. Verify that you will see:  This site has successfully sent a test message to the mail server.
6. Open your email inbox.
7. Verify that you will see an email with:
   • Title: [Your site name]: test message. Test email using XOAUTH2
   • Content: This is a test message to confirm that you have successfully configured your site's outgoing mail.

Initial setup - IMAP

1. Navigate to Site Administrator > Server > Email > Incoming Mail Configuration.
2. Set the following value:
   1. Enable incoming mail processing: Checked
   2. Mailbox name: the name before @ sign of your email address (Ex: Your email is abc@gmail.com, the Mailbox name will be: abc)
   3. Email domain: the name after @ sign of your email address. In this case, it will be: gmail.com
   4. Incoming Mail Server: imap.gmail.com
   5. OAuth 2 Service: Gmail - OAUTH2
   6. Username: The username that was used to connect to the Google Developer Console.
3. Save changes.
4. Navigate to Site Administrator > Server > Email > Message handlers.
5. Enable the Email to Private files.

Incoming mail testing

1. Create a new tab on your browser called Tab 1.
2. On Tab 1, click on the User Profile menu > Profile.
3. Observe the Email address of the admin user. (Example: xyz@gmail.com)
4. Create a new tab on your browser called Tab 2.
5. On Tab 2, open the webmail of the Admin's email (Example: https://mail.google.com)
6. On Tab 1, click on the User Profile menu > Private files.
7. Verify that you will see: You can also e-mail files as attachments straight to your private files space. 
8. Copy the email address.
9. On Tab 2, compose a new email with the following value:
   1. To: The copied email address.
   2. Subject: Test attachment
   3. Content: Attached
   4. Attachment: Attach an image on your machine.
10. Send the email.
11. Go to Site administration > Tasks > Scheduled tasks, locate Incoming email pickup task and click "Run now" link
12. On Tab 1, click on the User Profile menu > Private files.
13. Verify that you will see the image that you have sent via email.