Troubleshooting error messages that you receive when you are using OL and OE
http://support.microsoft.com/?kbid=813514

Have you ever been able to send using this account before?

To how many addressees was the original message sent?

If you don't use Incredimail (e.g., send from your account),
does this behavior persist?

Are you using a third-party firewall? If so, which one, and did you install
an update for it recently?

If you disable email scanning by your anti-virus application, does the
behavior persist? Email scanning provides no additional protection, it may
be the cause of the problem, and even Symantec says it's not necessary:

paste
Disabling Email Scanning does not leave you unprotected against viruses that
are distributed as email attachments. Norton AntiVirus Auto-Protect scans
incoming files as they are saved to your hard drive, including email and
email attachments. Email Scanning is just another layer on top of this. To
make sure that Auto-Protect is providing the maximum protection, keep
Auto-Protect enabled and run LiveUpdate regularly to ensure that you have
the most recent virus definitions.
/paste
http://service1.symantec.com/SUPPORT...02111812533106
--
~Robear Dyer (PA Bear)
MS MVP-Windows (IE, OE, Security, Shell/User)
AumHa VSOP & Admin; DTS-L.org


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?