Outlook maintains a "nickname" list that is used by both the automatic name checking and the AutoCompletion features. The nickname list is automatically compiled as you address email messages. If the nickname cache becomes corrupt, Outlook may not be able to identify recipients, may offer incorrect recipients, may send to an incorrect or old email address, or may send the message to the wrong person.

You may need to:

To delete a single cached entry:

In Outlook:

  1. Open Outlook.
    • Outlook 2010/2013/2016: On the Home page, click New Email.
    • Outlook 2007: Click New > Mail Message.
  2. Type one or more letters of the recipient name or address; this will show memorized (cached) entries in a drop-down list.
  3. Use the arrow keys on your keyboard to select the entry to be deleted. With the entry highlighted, press the DELETE key on your keyboard.
    This removes the entry from your autocompletion cache.

    Outlook for Windows

In Outlook for Mac 2011/2016:

  1. Open Outlook and click New email.
  2. Type one or more letters of the recipient name or address; this will show memorized (cached) entries in a drop-down list.
  3. Use the arrow keys on your keyboard to select the entry to be deleted. With the entry highlighted, press the DELETE key on your keyboard. Or you can click on the cross sign with your mouse.
    This removes the entry from your autocompletion cache.
    Outlook 2011 for Mac
    Outlook 2016 for Mac

In OWA:

  1. Click New (or New > Message)
  2. Type one or more letters of the recipient name or address; this will show memorized (cached) entries in a drop-down list.
  3. Use the arrow keys on your keyboard to select the entry to be deleted. With the entry highlighted, press the DELETE key on your keyboard.

    OWA delete cache

To delete a cached entry from Suggested Contacts in Outlook 2010/2013/2016:

Note: In a clean Outlook 2013 installation, Suggested Contacts folder is no longer available, the folder is never created, and no suggested contact items are created. In an upgrade to Outlook 2013, this folder is visible, and participates in linking, aggregation and search. However, no new suggested contact items are added to the folder. The folder displays in an upgrade scenario, but can be deleted.

  1. Switch to Contacts in the Navigation Pane.
  2. Open the Suggested Contacts folder.
  3. Find the entry you would like to delete.
  4. Right-click the contact and choose Delete.

    Suggested Contacts

    Note:
    You may use CTRL+A to select all Suggested contacts as well as CTRL and SHIFT keys to select several contacts.

To delete all cached entries:

In Outlook 2010/2013/2016:

  1. Navigate to File > Options > Mail.
  2. Scroll down to Send Messages and click Empty Auto-Complete list:

    Delete All Cached Entries
    • Alternatively, you can delete all cached entries using Outlook command-line switch. Close Outlook, go to Start > Run > type outlook.exe /cleanautocompletecache and hit Enter. On Outlook startup, choose your Exchange profile. It will be loaded without cached entries.

In Outlook 2007:

Outlook 2007 store this cache in a local, profile-specific file with the extension .nk2. To reset the Outlook nickname cache, use the following steps that are appropriate for your version of Microsoft Windows. After you restart Outlook, Outlook generates a new nickname cache.

Microsoft Windows Vista

  1. Exit Outlook.
  2. Click Start > Search.
  3. Click Advanced Search.
  4. Check the box for Include non-indexed, hidden, and system files (might be slow).
  5. Search for *.NK2 in the Name field.
  6. Right-click the .NK2 file with the name of the profile that you want to reset, and then click Rename.
  7. Rename the file to profile name.bak, and then press ENTER.
  8. Exit Windows Explorer.
  9. Restart Outlook.