SMTP relay by an external mail server

I want to relay from my exchange server 2003 by an external SMTP server with SMTP-AUTH, its a debian server with qmail, we use the exchange server only to exchange internal mail and send mail to external, to get mail we use the external mail server.So, to get the External SMTP Server, I go in the mmc: Server >> domain >> protocol >> Smtp and then in the properties I put in receipt >> advanced the domain and in HOST I write the SMTP host, then in receipt >> protection I have activated the "Standard Auth" and I wrote the UID and PWd of the remote server, but if I am trying to send a mail by the exchange server through the external mail server, then it doesnt goes with 553 error, but by looking in the external mail server, it looks like that the exchange server dont auth on the external mail server. Can anyone please help.

It is recommended that you set up Windows SBS by using the Configure E-mail and Internet Connection Wizard (CEICW). You may have to manually set up some settings in scenarios that aren't supported by the wizard. For more information on how to do that, follow the methods given on this website - http://support.microsoft.com/kb/825763/en-us

Hello - thanks for the useful info. I have troubleshooted with the provided links but get the following issue. I am using Outlook 2003 on SBS 2003 and when I try to send an e-mail to an external account I get the following error:

There was a SMTP communication problem with the recipient's email server. Please contact your system administrator.
<newemaildomain.net #5.5.0 smtp;553 sorry, that domain isn't in my list of allowed rcpthosts (#5.7.1)>

My basic setup is that I have SMTP connector relaying to a smarthost. This was working fine until we decided to change our business name. So what I did was I left the local network domain intact (LAN) as oldlocaldomain.net and ran CEICW to use newemaildomain.net. CEICW updated the e-mail addresses and I doublechecked the SMTP connecter as well as the SMTP Virtual server. But it won't let me send external mail via Exhchange. It will send to internal users via Exchange but not to external users. The smarthost is the same as always with port 2525 rather than port 25. Also I have set up a POP account to send and receive through the Smarthost - it work fine so smarthost seems ok.

Any ideas on what the issue is? Essentially I need my public email to be test@newname.net but but local LAN to remain as oldname.net.

Should I rerun CEICW to remove internet mail and start over?