When moving from Outlook 2007 to Outlook 2010 or 2013, saving your autocomplete addresses is a little tricky.

How to Import Auto-Complete List to Outlook 2010

In Microsoft Outlook 2010, the Auto-Complete List is no longer saved in a file with an extension of .nk2. The Auto-Complete List entries are now saved in your Microsoft Exchange Server mailbox or in the Outlook Data File (.pst) for your account. However, if you want to copy the Auto-Complete List (.nk2) from another computer that was using a POP3 email account or an older version of Outlook, you must import the file.

This info is available here http://support.microsoft.com/kb/980542

IMPORTING NICKNAME FILES TO OUTLOOK 2010

When you start Microsoft Outlook 2010 for the first time, your nickname cache (stored in the   profilename.nk2 file) is imported into a hidden   message in your default message store.

Note profilename is the name of your   Outlook profile.
For example, if you are using a Microsoft Exchange   account, the nickname cache is imported into a hidden message in the Exchange   mailbox.
Note Earlier versions of Outlook store the nickname cache .nk2 file in   the following folder.  

• Windows XP Drive:\Documents and Settings\Username\Application Data\Microsoft\Outlook

After the nickname cache is imported, the   profilename.nk2 file is renamed to   profilename.nk2.old. On the next start of Outlook,   your nickname cache is not imported. Outlook 2010 does not use the .nk2 file   for maintaining your nickname cache. All updates to your nickname cache in   Outlook 2010 are made to the hidden message in your default message   store.
Note If you have multiple Outlook profiles, the nickname cache from   each profile is merged into your new Outlook 2010 nickname cache on the first   start of Outlook 2010 by using that profile. Therefore, you may find more than   one .nk2 file renamed to .nk2.old.
However, there may be situations   where you have to import a nickname cache file after this first-run nickname   cache import process has finished. For example, a colleague wants to share   their nickname cache with you and you want to update your existing nickname   cache with your colleague’s data.

- To fix this problem automatically, Download the attached file. Click Run in the File Download dialog box, and follow the steps in the Fix it wizard.

Notes

• Please select an .nk2 file that you want to import into Outlook 2010.
• This wizard may be in English only. However, the automatic fix also works for other language versions of Windows.
• If you are not using the computer that has the problem, save the Fix it solution to a flash drive or a CD and then run it on the computer that has the problem.

-  To fix this yourself manually

To  import .nk2 files into Outlook 2010,   follow these steps:  

1. Make sure that the .nk2 file is in the following folder:
   %appdata%\Microsoft\Outlook
   NoteThe .nk2 file must have the same name as your current Outlook 2010 profile. By default, the profile name is "Outlook." To check the profile name, follow these steps:
   1. Click Start, and then click Control Panel.
   2. Double-click Mail.
   3. In the Mail Setup dialog box, click Show Profiles.
2. Click Start, and then click Run.
3. In the Open box, type outlook.exe /importnk2, and then click OK. This should import the .nk2 file into the Outlook 2010 profile. 
   Note After you import the .nk2 file, the contents of the file are merged into the existing nickname cache that is currently stored in your mailbox.

Note The .nk2 file is renamed with a .old file name extension on the first start of Outlook 2010. Therefore, if you try to re-import the .nk2 file, remove the .old file name extension.

If you are still experiencing problems with this - please open a helpdesk request for further assistance.  

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