We have Exchange 2003 running on a single server which also happens to be our file server with Active Directory users set up for everyone. Only a few of those AD users have Exchange mailboxes set up. The non mailbox users are in a different department and have their own email domain outside the server on a 3rd party host. The Exchange users have their own domain that is hosted on the Exchange Server. The problem is... the Exchange users cannot email to the non-Exchange users. EVERYTHING ELSE works fine! The Exchange Outlook clients will get an NDR saying the recipients mailbox does not exist at the organization (5.1.1) if they email the non-Exchange users. I even tried deleting the AD account for one of the users. I even created a new address at their domain hosting site, and I still received the same message. If one of our Exchange users emails anything to anyone at that particular domain, they get an NDR. Thank you for any support you can give!!!

Hi there, Off course they will get an NDR, and why is that, because the non-mailbox users have the same domain or email domain as your mailbox users, for example, if your exchange domain is User-Mailbox@domain.com , which is your internal exchange domain, and your hosting mailbox users also have the same email domain which is Non-MailboxUser@domain.com, now, when your user-mailbox users tries to send emails to users hosted thier mailbox outside your domain, your user will send to the same email domain which is authorized by your exchange server for internal users, so your exchange will search for these users internally and will never send the email to your SMTP Gateway or internet connector, cause the domain is sent for internal exchange domain. what you can do: create mailbox for all your users, including the one that hosted outside. modify the SMTP alias for your non-mailbox users to match thier SMTP address hosted outside, so they cansend emailsusing theoriginal email alias, for example, if one of the users called "Alaa Al-Ankar" which hosted outside have email addressas alankar@domain.com and when you create a userand mailbox for "Alaa Al-Ankar" and based on the default email policy on your exchange server, the smtp address for "Alaa Al-Ankar" becomes alaa@domain.com then, you need either to add alankar@domain.com as secondarysmtp address and then make it as the primary SMTP address and let the one that created by Exchange to be the seconday smtp address, or modifySMTP address for "Alaa Al-Ankar" to be alankar@domain.com, so Alaa can stillsendemails with the correctSMTP alias, and can recieve emails via your hosted domain for that SMTP address. then configure all your user's outlook to connect to your exchange server to connect to thier mailboxes created on exchange. for the users that hosted outside, you can add thier account in thier outlook, and let these users pulls thier emails directly from thier outlook, and when they send email, you can configure your exchange server to send all external emails. by this, you can send and recieve emails internally for all your users, and for the hosted users, they can still recieve the emails from the hosted mail service, and they can save all these emails into thier mailbox created on your exchange server. please let me know if the above steps helped you in solving your problem.

I started to do as you said, but then I realized that not every one of the non-mailbox users was using Outlook. Some are using Outlook Express and some are using Windows Mail that comes with Vista to check their outside-hosted email via POP3. I am new to Exchange Server, so I don't know how everything works yet. Could they still connect to the Exchange Server? However, I did discover that the hosted domain was indeed listed in the Default Email Policy as @outsidedomain.com and the primary SMTP was @insidedomain.com. I just deleted the @outsidedomain.com entry and it worked. Thank you!

Aha, so here is the problem. my assumption was not correct, I assumed that the internal and external domains are the same for mailbox and non-mailbox users. and the reason why your exchange was returning an NDR cause it was authoritative for the external domain as well, so it was searching the local GC for the mailbox server for the destination address and when it didn't find any recipient for it it returns an NDR and it will not deliver it to SMTP for external delivery via Internet Connector or any external connector configured on your Exchagne. since you removed the EAP (Email Address Policy) for your external domain from exchange, now exchange will treat this domain as external domain and will send it to your Internet Bridge Head or SMTP Gateway Server that configured on your Exchange. now for your case, if you want your Exchange Server to be authoritative or responsible for outisde domain delivery , then you have to return back the SMTP Address for the outside domain in the Default Address Policy where this will be applied to each and every email users under your exchange server, or if you want to let certain users to have the @outsidedomain.com SMTP address, then you have to create a condition in the Email Address Policy that you created for this outside domain. if you want i can provide you witth the steps for how to do this, but first i want to know if you would like to have both domains hosted by your exchange , and the internal and external domains will be Exchange responsibilities. regarding to non-outlook users, that they connect to thier outside mailbox using POP3 , please note that after adding these users to your exchange server , there is no need for these users to connect using POP3 due to the unsecure connectivity provided by POP3, also you need to know that by Default, when you install Exchange Server 2003 , POP3 and IMAP4 Services and protocols are disabled, if you really need to enable these protocols then you need to secure them. One final thing, I want to inform you that Microsoft Exchange Teams posted all kinds of Exchange documentation under Microsoft Exchange Site, I personally downloaded all these documents , and checking even for updated documents from them, they did a great job for generating such documents, they covered all what Exchagne Administrators, Implementors, Architects, End Users who wants to know what is Exchange , etc, in other words, all what you need to know and learn from A to Z can be found under this site. so i advice you to go and start downloading these documents from this site: http://technet.microsoft.com/en-us/library/bb123872.aspx please let me know if you need any more help.