Using Outlook 2003 with Exchange 2010

Over the last few months I’ve been working with a number of clients migrating from Exchange 2003 to Exchange 2010, one of the questions that comes up regularly during design workshops is “can I still use Outlook 2003?” Well the official answer is that Outlook 2003 is supported for use with Exchange 2010, but the reality is a little less straightforward.

There are a number of issues that need to be taken into account and considered before rushing into that upgrade to Exchange 2010 if you are still running Outlook 2003.


I’ll start with an easy one, if you are using Exchange 2010 RTM, then there is a requirement to use encryption between Outlook clients and the Exchange 2010 Client Access server. Outlook 2003, by default, doesn’t have this option enabled. This is simple to resolve by, manually or by Group Policy, enabling encryption within the Outlook Account settings as explained in this Microsoft KB item As mentioned in the article, this requirement is removed with Exchange 2010 Service Pack 1.

Slow updates

This is the “Big One”, Outlook 2003 expects Exchange to send User Datagram Protocol (UDP) notifications to update Outlook, this functionality has been removed from Exchange 2010! The result is delays to folder updates  (e.g. Outbox showing unread messages for a while, Errors when deleting a message for the second time, after it has already been deleted but not refreshed, etc) as Outlook 2003 reverts to Polling every 60 seconds for folder updates.

Now, according to this has been resolved by Update Rollup 3 for Exchange Server 2010 Service Pack 1 and a simple Registry entry modification on the Client Access Server. This is not the case, the problem is reduced but not resolved.

Further investigation uncovers an Interim Update relating to KB2579172, which can be made available if you call Microsoft Support (although they might deny it!), this appears to fix the issue and was due to be included in Update Rollup 6 for Exchange Server 2010 Service Pack 1.

A contact I have inside Microsoft has informed me that this IU has now been dropped from UR6 due to issues with the RPC Client Access service crashing, and will probably now come in SP2 Rollup 1…..Watch this space.

Instance-<GUID> in Outlook profile

I’ve only seen this issue once personally, but on discussing it with some other clients they had also seen similar behaviour.

Outlook 2003 is working perfectly connected to Exchange 2010 and then reports “The connection to the Microsoft Exchange Server is unavailable. Outlook must be online or connected to complete this action.” If you check the Account Settings the Exchange Server Name is Instance-<GUID>.

Re-entering the correct Exchange Server Name resolves the issue until next time.

Microsoft have a hotfix available at to resolve this, but it needs to be applied to every instance of Outlook 2003 experiencing the issue.

Open multiple 2010 mailboxes from Exchange 2003 mailbox

This only occurs during a coexistence phase between Exchange 2003 and Exchange 2010. If a mailbox user hosted on Exchange 2003 attempts to open More that one folder or mailbox, hosted on Exchange 2010 they may receive one of the following error messages:-

“The set of folders could not be opened” or “The information store could not be opened”

Once again there is a Microsoft Hotfix for the Exchange 2003 Server at if you are experiencing this exact problem.
So, can you use Outlook 2003 with Exchange 2010? You can and you might have no issues at all, but, you could also end up dealing with some or all of the above issues. My best advice would be to upgrade to Outlook 2010 if you can, that way you will gain all the benefits of Exchange 2010, with none of the issues of supporting Outlook 2003.