Outlook freezes when composing a new email or replying

Applies to: Outlook 2016Outlook 2013Microsoft Outlook 2010 More


Microsoft Outlook freezes when you try to compose a new email or reply to an email.


This issue may occur if Outlook is configured in Online mode and you have a large nickname cache.


To work around this issue, use one of the following methods.

Method 1: Manually remove individual entries from the nickname cache

  1. In Outlook, open a new email message.
  2. Type the first few characters of a nickname cache entry that you want to remove from the cache.

    Note If you are not sure which nickname cache entries that you want to remove, start by typing 'A' to see all the entries that begin with that letter, and then remove any items that you no longer want by following the next steps. Then type 'B' and repeat these steps for all the letters alphabetically.
  3. When the entry appears in the list of suggested names, move your mouse pointer over the name until it becomes highlighted, but do not click the name.
  4. When the “X” icon appears next to the highlighted name, click X to remove the name from the list.
  5. Repeat steps 2 - 4 as necessary.
Note The number of nickname cache entries that you must remove to prevent the issue will vary. Try to remove several nickname cache entries by using these steps, and then test for the issue. If the issue still occurs, remove several more, test again, and repeat as needed.


Method 2: Reduce the size limit of the nickname cache

The default nickname cache limit for Outlook 2016, Outlook 2013 and Outlook 2010 is 1,000 entries. When you reduce the limit, the least used nickname cache entries will be removed from the cache. Follow these steps to reduce the limit.

Follow the steps in this section carefully. Serious problems might occur if you modify the registry incorrectly. Before you modify it, back up the registry for restoration in case problems occur.
  1. Exit Outlook.
  2. Start Registry Editor.
    • In Windows 10, Windows 8.1 and Windows 8, press the Windows Key + R to open a Run dialog box. Type regedit.exe and then click OK.
    • In Windows 7 and Windows Vista, click Start, type regedit in the Start Search box, and then press Enter.
  3. Locate and then select the following registry subkey:


    NoteThe placeholder x.0 in this registry subkey represents your version of Microsoft Office. Use the appropriate value from the following list.

    Outlook 2016, Outlook for Office 365 and Outlook 2019 = 16.0
    Outlook 2013 = 15.0
    Outlook 2010 = 14.0
  4. On the Edit menu, point to New, and then click DWORD value.
  5. Type MaxNickNames, and then press Enter.
  6. On the Edit menu, click Modify.
  7. Select Decimal.
  8. Type the new value for the limit, and then click OK.

    Note The value for the limit that you must specify to prevent the issue will vary. Try decreasing the limit by only a marginal amount to test the new limit. For example, decrease the limit by 10 percent decrease by specifying 900 for the MaxNickNames value. If the issue persists, decrease the limit by another 10 percent of the original default value by specifying 800 for the MaxNickNames value. Repeat this until the issue no longer occurs.
  9. Exit Registry Editor.
  10. Start Outlook.

Method 3: Configure Outlook in Cached Mode

  1. In Outlook, on the File menu, click Account Settings, and then click Account Settings.
  2. Select your Exchange account, and then click Change.
  3. Click to enable the Use Cached Exchange Mode option.
  4. Slide the Mail to keep offline setting to the setting that you prefer.
  5. Click Next.
  6. On the prompt that the operation you selected will not complete until you quit and restart Microsoft Outlook, click OK.
  7. Click Finish, and then click Close.
  8. Exit and then restart Outlook.

Method 4: Empty the nickname cache

These steps removes every entry in the nickname cache. You cannot automatically restore the nickname cache after it is emptied.
  1. In Outlook, on the File menu, click Options.
  2. Select the Mail tab.
  3. Scroll approximately halfway down until you see Send messages.
  4. Click Empty Auto-Complete List.
  5. Click Yes to confirm.
  6. Click OK.