Did you just receive some mail notifications saying that mail could not be delivered to
firstname.lastname@example.org? Fear not. This isn’t some kind of weird hack or compromise of your system. In all likelihood, someone just compiled PHP on the server.
PHP’s unit test to confirm that bug 72463 remains fixed makes two
mail() calls that try to send mail to that address. The email address was specifically chosen to ensure that it would not refer to a real email address while still remaining a valid email address, thus the reason for the mail handler on the server sending the error stating that the mail could not be sent.
So, there’s no problem. It’s just PHP’s unit tests doing their job when someone runs