Recently, I’ve been learning about email and how to set things up so people can’t impersonate email addresses.
One of the things to set up is DKIM, which is a method of “signing” an email as it leaves your server. The recipient end can validate that signature when email is received, and if it fails the validation, the email can be rejected as not legitimate.
This site can be used to test if your DKIM signature is set up correctly:
Another way to test is to send it to your Yahoo email, then look at the message source. If you find “dkim=pass” in the header, you’re good to go.
And, one more way is to send an email to firstname.lastname@example.org and you’ll get a report back.
Additional resource: https://emailstuff.org/