I'm the IT Guy for a small company with about 50 computers. One computer is having Outlook Problems. The user can receive emails fine, but is unable to send, getting the message 503, No Recipient, even though it's a valid address. I've tried doing several things to fix, but haven't been successful.

Here's what I tried in various combinations.

-Set the Outgoing Server to Require Authentication while using the same settings as the incoming mail server
-Changed the Outgoing Server from 25 to 465
-Cleared internet settings and reset web/sercurity settings back to default

I enabled and viewed the OPMLog and here is what I received for errors:

2009.01.12 11:10:12 SMTP (mail.company.com): <rx> 550-Verification failed for <*****>
2009.01.12 11:10:12 SMTP (mail.company.com): <rx> 550- Unroutable address
2009.01.12 11:10:12 SMTP (mail.company.com): <rx> 550 Sender verify failed
2009.01.12 11:10:12 SMTP (mail.company.com): [tx] DATA
2009.01.12 11:10:12 SMTP (mail.company.com): <rx> 503 No recipient(s).


2009.01.12 11:10:12 SMTP (mail.company.com): End execution

I appreciate any additional suggestions to correct! Outlook 2003, SP3, with XP

Try switching the outgoing port to 587.

Looks like your outgoing server requires authentication. Follow these steps for Outlook 2007.

On the main menu in Outlook go to tools>Account Settings>Change>More Settings>Outgoing Server>Then check the box that says 'my outgoing server (SMTP) requires authentication'.

That's it you're done it should now work. What this does is it automatically authorises the outgoing server to the right port set by your mail server.