Tip: App passwords aren’t recommended and are unnecessary in most cases. To help keep your account secure, use "Sign in with Google" to connect apps to your Google Account.

An app password is a 16-digit passcode that gives a less secure app or device permission to access your Google Account. App passwords can only be used with accounts that have 2-Step Verification turned on.

When to use app passwords

Tip: iPhones and iPads with iOS 11 or up don’t require app passwords. Instead use “Sign in with Google.”

If the app doesn’t offer “Sign in with Google,” you can either:

• Use app passwords
• Switch to a more secure app or device

Create & use app passwords

Important: To create an app password, you need 2-Step Verification on your Google Account.

If you use 2-Step-Verification and get a "password incorrect" error when you sign in, you can try to use an app password.

1. Go to your Google Account.
2. Select Security.
3. Under "Signing in to Google," select 2-Step Verification.
4. At the bottom of the page, select App passwords.
5. Enter a name that helps you remember where you’ll use the app password.
6. Select Generate.
7. To enter the app password, follow the instructions on your screen. The app password is the 16-character code that generates on your device.
8. Select Done.

If you’ve set up 2-Step Verification but can’t find the option to add an app password, it might be because:

• Your Google Account has 2-Step Verification set up only for security keys.
• You’re logged into a work, school, or another organization account.
• Your Google Account has Advanced Protection.

Tip: Usually, you’ll need to enter an app password once per app or device.

In Joomla Server Configuration:

https://prnt.sc/_noxlEUZtNgC

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IF after all this you are getting a ? by the email received from the email address you have been working on, go to postmaster.google.com and add the domain to the list, copy the text record and add it to the DNS Zone Editor for that domain. Go back to postmaster.google.com and then click o Verify to make sure the text file has been recognised.

Thanks to Tim from Cyber Salt for providing this last piece of information which was not provided by the Google representative who helped me with the initial setup.

https://www.youtube.com/watch?v=eLdiSanEvmw