gmail smtp server settings

Hi Frannygirl,

have you tried to remove the account and then add it again?

Here is a brief guide to remove an account

1. In the Mail app  on your Mac, choose Mail > Preferences, then click Accounts. 
2. Select an account, then click the Remove button .

Note: If the account is used by other apps on your Mac, you’re asked to remove the account in Internet Accounts System Preferences. Click the button to open Internet Accounts, then deselect the Mail tickbox for the account. To stop using the account in all apps, make sure the account is selected, then click the Remove button.

Here is a complete guide to Add an email account to Mail on your Mac - Apple Support

If you can’t send or receive email on your Mac

It may just need an App Password separate from the gMail password…

https://support.google.com/mail/answer/185833?hl=en-GB