though the following might not be applicable to absolutely all server setups the following should apply to most if you want to use gmail for SMTP delivery (wppizza->settings->SMTP section)

SMTP Host: smtp.googlemail.com
SMTP Port: 465
SMTP Encryption: SSL
SMTP Username: [email protected]
SMTP Password: generate according to instructions below. your “normal” sign-in password is not likely to work – especially if 2-step verification is enabled on your google account

Visit your App passwords page. You may be asked to sign in to your Google Account first.

At the bottom,

1. “Select app” -> “Other” -> enter a name of your choice -> click “GENERATE”
2. make a note of the password generated (it will be the only time you will ever see this password !)
3. click “DONE”
4. enter the password generated under 2 into the “SMTP Password” field

Note: passwords are stored encrypted and are not displayed after saving.
However, you will see something like “a password has been set.” next to the SMTP Password field.
Furthermore, you can also test your SMTP settings before actually saving.