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One of the most common questions on forums is why does a user get a NDR (Non Delivery Report) report similar to the one below when they send an appointment to another person. The NDR will reference a user who is no longer part of the company and does not have an account on the system any longer.

Your message did not reach some or all of the intended recipients.
Subject: Sales Meeting
Sent: 8/22/2008 8:54 AM

The following recipient(s) could not be reached:
Another User on 8/22/2008 8:54 AM
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.
<mail.example.net #5.1.1>

This is caused by delegates.
The user referenced in the NDR was a delegate on the recipient of the appointment.

However what you may find is that when you look at Delegates through Outlook, the user is not listed.
This is because the delegate system can get "stuck" and the information in Outlook and on the server are not in synchronisation.

To reset it, simply follow the procedure below.

1. Remove any delegates that are currently listed for the user.
2. Add a new delegate to the list. IMPORTANT - this new delegate must not have been a delegate to the user before. I will usually create a temporary mail enabled account for this process and then delete afterwards.
3. Wait at least 30 minutes for this change to be propagated to the server correctly.
4. Remove the new delegate from the list.
5. Wait at least 30 minutes again.
6. Add the preferred delegates back in to the list.

This works by replacing the complete list of delegates on the account.

If this still doesn't work then you will have to scan the domain using adsiedit.msc for references to the former user on the user's settings. I have only ever had to do that once, when Outlook wouldn't open the delegates tab. Otherwise the procedure outlined above has always worked for me.

There have been a number of posts on forums about the database limits in various versions of Exchange. This post is a quick summary.

The limits shown also apply to Small Business Server, which has Standard edition of the relevant version installed.

Exchange 2000 Standard Edition: 16gb *
Exchange 2000 Enterprise Edition: Unlimited **

Exchange 2003 Standard Edition RTM and SP1: 16gb *
Exchange 2003 Standard Edition SP2: 18gb soft limit, 75gb hard limit ***
Exchange 2003 Enterprise Edition: Unlimited **

Exchange 2007 Standard Edition: 50gb soft limit, unlimited hard limit ***
Exchange 2007 Enterprise Edition: Unlimited **

* Exchange 2000 and 2003 Standard edition SP1 or older, can both be increased to 17gb as a temporary measure to allow the store to be remounted to remove content.

** The actual maximum possible size of the Exchange database is 8TB, effectively unlimited.

*** Exchange 2003 SP2 and Exchange 2007 have soft limits. This is a setting in the registry that limits the database to the size shown. It can be increased as required.
The idea is to stop run away store growth. Should something happen within the Exchange setup that causes rapid store growth, it will hit this limit and be dismounted.

With this introduction of a soft limit, the way that the database limit is enforced was changed.
With Exchange 2000 and 2003 prior to SP2 the database limit was the physical size of the store. The amount of white space in the store was not taken in to account. This meant that once you hit the limit you needed to do an offline defrag of the database to get it below 16gb, even after you had removed content.

With Exchange 2003 SP2 and later, this behaviour has been changed. The limit is now the physical size of the store, minus the amount of white space. Therefore if you hit the physical limit of 75gb on Exchange 2003 SP2 then an offline defrag is not going to help. Users need to actually remove content to create white space in the store.
Furthermore the database size is not checked in real time. It is checked once a day, by default at 5am (this can be changed via a registry modification). Therefore if the store dismounts because the limit has been breached, you can simply restart the service and the store will mount again.

However in my experience, once you hit the limits, even removing the content will only be a temporary solution. Either an investment needs to be made in an archiving solution that actually removes the content from the store, or an upgrade to Exchange 2003 Enterprise edition or Exchange 2007 Standard needs to be carried out.

Relevant Links at microsoft.com

Exchange 2003 Limit Changes: http://technet.microsoft.com/en-us/library/aa998066.aspx
Exchange 2007 Limit Changes: http://technet.microsoft.com/en-us/library/bb232092.aspx

Increase the limit of the Exchange 2000 database to 17gb: http://support.microsoft.com/kb/813051