Why am I getting email bounces that say "451: Could not complete sender verification"?
It isn't us, it's the server at the other end who was trying to send email to you...
In short, our mailservers check to confirm an email address trying to send mail to you is reachable
before accepting the email. This is in order to conform to the internet RFC's
(published standards). It also verifies that if we need to send a bounce
message back to you, we are able to do that (instead of the email going into
a black hole in cyberspace with everyone wondering what happened to the mail). Finally,
as a side effect it also blocks lots of spammers and viruses that send email
with forged From: addresses (e.g. "123jhdwf32087@yahoo.com")
We can disable this check for your domain, but two things will happen: Email
for your domain will be slightly less reliable (since we can't verify whether
bounces or replies will work), and you will start getting orders of magnitude
more spam and viruses than you do currently.
We recommend talking to the folks at the mailserver
at the other end (the one trying to send the mail to you).
