scott m wrote:

I just downloaded a trial version of outlook 2007. I am receiving my messages
fine but when I attempt to reply I get the following message:

Your message did not reach some or all of the intended recipients.

Subject: test
Sent: 11/26/2009 9:27 PM

The following recipient(s) cannot be reached:
'Mijares' on 11/26/2009 9:27 PM
503 Valid RCPT command must precede DATA

When you reply (but before you send), is the e-mail address valid that is
shown in the To/Cc/Bcc fields?

Tried disabling the superfluous scanning of your e-mails by your anti-virus
program?