550 5.7.1 Unable to relay

Check privileges for the sender and resend the message. Try using OWA and check if user can send message to outside domain. Also try n send message manually.

Thanks
Kunal

How are you configuring your travelling users? Are you trying to use POP3/SMTP?
If you have Exchange 2003 on Windows 2003 in a Windows 2003 AD domain and the clients are Windows XP SP2 and Outlook 2003 then you should be using RPC over HTTPS. It will provide your remote users with the full benefits of Exchange/Outlook without requiring a VPN. Combined with cached mode in Outlook 2003 your remote staff will be fully functional wherever they may be.

Otherwise need to know a lot more about how you are trying to setup your remote users. You have missed out most of the vital information. While this is the Exchange TA, there are three (four including E12) versions of Exchange, five versions of Outlook involved, using three different versions of Windows. Each combination brings different issues.

Simon.

We have a 2k exchange server in a 2K domain.  I'm trying to set it up through pop3 using Outlook 2002.  When I go to a diff location than our office and use the pop3/smtp settings I can also send to people within our domain, but not to anyone outside the domain.

Sorry for the lack of information in post.

If you are using POP3/SMTP then have you configured Outlook to authenticate when sending?If you don't do that then it will not allow email to be sent out to external hosts.

Simon.

When in the Outlook settings, I click the more settings button, click outgoing server, check smtp requires authentication, log on using, and  then I provide the credentials for logging onto the domain, user@domain and the password.  This works while in the office but not outside the office.  Outside the office you can only send to individuals within the domain.

Should be no difference whether you are inside or outside of the network.
Have you enabled relaying for a range of IP addresses as well? That is checked first, so authentication may not be used.

Try authenticating in the format of domain\username and see if that makes any difference.

Simon.

Since the employees I'm trying to setup will be travelling the range of IP addresses I'd be targeting could be any range that the US uses. I thought the checkbox for "Allow all computers which successfully authenticate to relay" would resolve the issue.

I didn't mean IP range for that reason - I meant with allowing relaying internally - as a reason for why it works inside but not outside. Allowing relaying by IP address is usually a very bad idea and I try to avoid it where possible. It is too easy to turn yourself in to an open relay.

Simon.

How do I check this?