Microsoft Outlook generates and maintains a nickname list that is used by both the automatic name checking and the automatic completion features. If the autocomplete cache is corrupted, Outlook may be unable to recognise recipients, offer incorrect recipients when automatically completing the e-mail address, send the message to the wrong person or not send the message at all replying with an instant bounce back “None of your e-mail accounts could send to this recipient”.

Unlike earlier versions of Outlook that store the nickname cache in a NK2 file on your hard drive, Outlook 2010 stores the nickname cache in your primary message store. If you are using a Microsoft Exchange Server account, your nickname cache is stored in a hidden message in your mailbox. This allows the autocomplete feature to be retrieved from any computer you may use your email from.

If you are receiving the bounce back like the one shown below and your autocomplete cached has become corrupt we can clean it, unlike earlier versions of Outlook simply renaming the autocomplete file won’t fix the issue as the list will be downloaded again next time you open Outlook.

From: System Administrator
Your message did not reach some or all of the intended recipients.
The following recipient(s) cannot be reached:
'name@domain' on 17/09/2011 12:30
None of your e-mail accounts could send to this recipient.

Before clearing the autocomplete cache you may wish to backup the file. The autocomplete file can be found in the following location C:\Users\%username%\AppData\Local\Microsoft\Outlook\RoamCache\Stream_Autocomplete*.dat. You can quickly locate this folder by pasting %APPDATA%\Microsoft\Outlook into Windows Explorer or the Run dialog. Now copy and rename this file for safe keeping.

You can now safely clear the autocomplete cache by following one of the methods listed below:

Method 1

• With Outlook 2010 open, click File > Options
• Click the Mail tab
• Under Send Messages, click Empty Auto-Complete List

Outlook will generate a new nickname cache.

Method 2

•     Click Start > Run.
•     Launch Outlook with the clean autocomplete switch – Outlook.exe /CleanAutoCompleteCache

Note If Outlook is not installed in the default location, you must point to the path of Outlook.exe.

Outlook will generate a new nickname cache.