Problems sending to external POP3 from Exchange server

[Sheldon]

I am having problems sending email from an Exchange server
to an external POP3 email account. In some instances, both
the Exchange and POP3 accounts have the same email
addresses. IN other cases, I am sending to an external
email that does not exist on the Exchange server. Even
though I have the POP3 account set as the default,
external emails are still trying to send through the
Exchange server and are getting rejected:

The e-mail account does not exist at the organization this
message was sent to. Check the e-mail address, or contact
the recipient directly to find out the correct address.
<XXXXX.xxxxx.xxxxx(exchange server address)
#5.1.1>

Is there any way to configure either Outlook or the
exchange server to send this email correctly?

Thanks,

 

[Sheldon]

I have just completed a rollout of Outlook 2002. None of
the users having this problem experienced it in Outlook
2000. However, since "upgrading" to Outlook 2002 the
problem started. The weird part of the problem is that it
does not occur for all users, it seems to be fairly random
for the users it affects. An additional note, I have
compared Outlook setting on one the works and one that
fails, and the settings appear to be indentical.

RE:Selecting the external account from drop down
list.....This does work for users having this problem, but
my confusion is....why is it happening to only some users
and not all???

Thanks,
Sheldon