Understanding how AutoComplete works in Outlook 2010

Microsoft Outlook will automatically suggest a recipient in the To, CC, and BCC fields of a new email message based upon previous recipients that you have sent mail to in the past.  In versions prior to Outlook 2010, these were stored in an NK2 file that was stored in your user profile on the PC where you were running Outlook.  Starting with Outlook 2010, this auto-complete cache is stored in your Inbox on the Exchange server (if you are running in a Microsoft Exchange environment) so that the auto-complete cache will contain the same information when using OWA, Windows Mobile, or Outlook 2010 on another PC.

I have been asked “How does the Auto-Complete work regarding what information it searches against?”  For example, if you type certain information, such as the display name, or the primary email address, it suggests the correct recipient.  However, if you type other information, such as last name, it does not.  I did some research on how this works, and here is what I found.

Let me start by defining some terms.  Auto-Complete is the feature that accesses a cache file that contains the recipients you’ve sent to or resolved already, it doesn’t search live against AD or the GAL.  It refers to the pop-down menu when you type on the “To” or “CC” line in a new message, as shown in the following screenshot:

Auto-Resolve refers to the feature that resolves the recipient’s name when you hit either “CTRL+K” or “tab” when typing information on the “To” or “CC” line.

Auto-Complete Behavior

By default, the Auto-Complete cache in Outlook is empty.  It starts recording addresses in the cache as soon as you start resolving them (using auto-resolve via CTRL+K, or by inserting addresses from the Global Address List or Contacts).  These resolved addresses are only stored in the auto-complete cache during the current Outlook session and are purged as soon as you exit the application, unless you actually send a message to these recipients.  Once you send a message to them, they are kept in the auto-complete cache semi-permanently (more on this later).

Consider a user named Jane Doe.  Her username is jdoe, her primary email address is jane_doe@domain.com, her Exchange Alias is janedoe, and her display name is “Jane K. Doe”.  When searching for a recipient based on text you type in the “To”, “CC”, or “BCC” fields, auto-complete looks at the following fields:

1. Display Name (i.e. Jane K. Doe)
2. Primary SMTP E-mail address (i.e. Jane_Doe@domain.com)
3. Exchange Alias (i.e. janedoe)
4. legacyExchangeDN attribute in Active Directory (more on this later)

Auto-complete does NOT search against any of the following criteria:

1. First Name (if it is different from the display name, for example if the display name contained a nickname instead of the legal first name, which is listed in the recipients’ “first name” field in Active Directory)
2. Last Name (unless one of the above four fields starts with the last name)
3. Username (unless one of the above four fields starts with the username, or is set to match the username)

Auto-Resolve Behavior

Auto-Resolve can query multiple fields beyond the limitations of the fields that Auto-Complete works with.   There is a good chart of the fields that Auto-Resolve uses when Outlook is in offline mode vs. online mode here.

How long is a recipient’s information kept in the Auto-Complete cache?

In Outlook 2003 and 2007, the cache file (NK2 file) could store up to 1000 recipients in it.  Once it hit this limit, it would start to purge old recipients in the order that they were added (keeping the most recently used).  I have been unable to find out if the Outlook 2010 cache has a similar limit.  If anyone has any information regarding this, I would encourage you to leave it in the comments.

More information

For information about clearing the Auto-complete cache:

http://support.microsoft.com/kb/287623

http://aspoc.net/archives/2010/05/04/how-to-clear-the-autocomplete-list-in-outlook-2010/

For information on the legacyExchangeDN Active Directory attribute:

http://www.msexchange.org/tutorials/Understanding-LegacyExchangeDN.html

Outlook Rules and Email Aliases

At my company we recently switched from Lotus Notes to Microsoft Outlook 2010 with Microsoft Exchange 2010 running on the back end.  The transition was very smooth thanks to the knowledge and skill of our Email Systems Administrator, however there was a new “feature” of Outlook/Exchange that posed a problem concerning some rules.

Our SCOM 2007 installation is setup to send notification emails with the address SCOM_Admin@ourcompanydomain.com.  This SMTP email address is configured as an alias for my mailbox, although it is only a secondary address, not the primary.  So, when I send an email, the Internet header shows that the message was sent from my public email address.  Several people on my team, who are configured to receive email notifications from SCOM, have a rule setup (that was also configured in Lotus Notes) to move messages received from the SCOM_Admin address to another folder.  This worked fine in Lotus Notes, but Outlook and Exchange like to resolve this address in the rule to a specific recipient in the Exchange Global Address List.  The result is that whenever I send an email to anyone with this rule in place, my email messages are routed into the SCOM folder instead of arriving in their inbox.

The easiest way to fix this was to use the rule condition “with specific words in the message header” instead of the “from people or public group” condition in Outlook.  For the specific words, I put in the email address for my secondary SCOM_Admin address, and it works.  The rule should look something like this: