I get the following rejection message when sending an email to a friend of mine. Can you tell me how to fix this? This started about a week ago. No changes were made to my friends email account. """ Your mail could not be delivered because the recipient is only accepting mail from specific email addresses."""

I think your friend needs to go in and check their settings closer... again. Don't assume nothing changed. And don't assume it couldn't change without direct intervention.

Not just the email application... but their Internet protection software as well.

It's possible your friend has set up a whitelist-only feature on their email.