Link here: https://wiki.debian.org/Exim4Gmail
Mostly good advice.
Choose “YES” for “Hide local mail name in outgoing mail?”.
The answer to the next question is “localhost”
Ignore the part about: Edit your address rewrite table /etc/email-addresses
use 2FA in Gmail. Create an App password and use that.
SMTP server is now smtp.gmail.com in /etc/exim4/passwd.client as of 2019-10-16.
WordPress plugin to change from… https://wordpress.org/plugins/wp-change-default-from-email/