450 server error:
Requested mail action not taken: mailbox unavailable



This response is sent by the server to indicate that a message could not be
addressed to a locally hosted recipient because the mailbox/mail address is
not valid.
----------------------------

That's a generic statement really, indicating that the mailbox isn't
available for whatever reason. Could you be mis typing the addresses? Or
have them stored wrongly spelled someplace?

Also notice the "tempfail"; may be it's temporary thing. Maintenance,
whatever.

Just a thought,

Pop`





Larry wrote:
Using OE6 I was sending an e-mail to an address I've often sent to
before, using my AT&T Internet connection, and instead of the e-mail
being sent I got this message (I've changed the e-mail address to a
generic name with the same form and the subject to "Subject name"):

The message could not be sent because one of the recipients was
rejected by the server. The rejected e-mail address was
'. Subject '[Subject name]', Account:
'ipostoffice.worldnet.att.net', Server: 'imailhost.worldnet.att.net',
Protocol: SMTP, Server Response: '450 [TEMPFAIL] destination not
valid within DNS', Port: 465, Secure(SSL): Yes, Server Error: 450,
Error Number: 0x800CCC79

This happens from time to time: addresses I've successfully sent to
many times will suddenly cause this error message, and then at a
later point I can send to them again. It's not a permanent issue,
but it's very annoying when it happens.

What is the explanation for this?