Configure Outgoing Mail Server with Gmail

First of all Login in to Your Gmail Account.
And then Go to the My Account Section https://myaccount.google.com
Open the Security tab in the Sidebar.
Then You can see There is a 'Sigining in to Google' section, Make Sure you have turned on two steps verification if Not Then Turn On two steps verification.
When You Turn On Your 2-Step Verification then you'll be able to see the App Password option.
And Now Click on App Passwords. Then select app as Mail and select your corresponding device as others and give any name (eg: Odoo).
Then Click on Generate to create App Password.
Now your app Password is been created
Goto Odoo, Settings > Technical > Outgoing Mail Servers > Open the record and replace your password with the app-generated password and Test Connection