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Command-line switches to troubleshoot Outlook 2010 problems

Are your users experiencing Outlook problems? These five command-line switches will help identify and remedy the cause.

Pinpointing the source of problems in Outlook 2010 can be tough, but there are some command-line switches that...

help identify and repair the Outlook problems admins deal with on a daily basis.

Since Microsoft Outlook 2000, administrators have had the option to start Outlook with a variety of command-line switches that are appended to the outlook.exe command. There are multiple switches to choose from, so be sure to check out Microsoft’s full list of command line switches for Outlook.

Here are the five most important switches to keep in mind when troubleshooting an Outlook error.

1. /safe. Arguably the most popular switch of all, safe mode starts Outlook with its most basic settings. In the same way that launching PCs in safe mode involves minimal services, the /safe switch opens Outlook with only its most basic settings in-tact, without any add-ons enabled.

There’s a long list of add-ons that you can install on your Outlook client -- some good, but many bad. This includes any antivirus and antispam applications that install add-ins to Outlook to scan your users’ incoming and outgoing email. If Outlook is having issues launching or is crashing intermittently, starting in safe mode will help you identify if an add-on is causing the issue and needs to be removed.

You can start safe mode followed by a number (1, 3 or 4). For example, outlook.exe /safe:1. This makes Outlook start in safe mode with specific options enabled, allowing for more granular safe-mode troubleshooting.

2. /rpcdiag. One of the most troublesome Outlook setups is Outlook Anywhere (formally known as RPC over HTTP). With the increasing popularity of hosted Exchange setups, this switch has become increasingly popular for troubleshooting connections to hosting providers.

Wen you start Outlook with the /rpcdiag switch, a dialog box opens to display Outlook’s connection status. The dialog box explains that either the connection to Exchange Server is continually failing or that connection requests are being dropped. It also displays which network interface it uses to connect.

If Outlook is stuck on “Trying to connect to Exchange” and you want to actually see Outlook’s connection status, you can use the /rpcdiag switch. You can also access this switch when Outlook is loaded by holding down the ctrl key and right-clicking the Outlook icon, then selecting Connection status.

3. /cleanrules. You can set up rules within your Outlook (client rules), while rules are applied by default through Exchange (server rules). Available since Outlook 2003, the /cleanrules comes in handy when troubleshooting Outlook.  

As rules build up within Outlook, the client and server rules may begin conflicting and you’ll be prompted for which set should take precedence. The /cleanrules switch restores the default client and server rules, letting you start over and get your rules in order. You also have the option to specifically clean the client or server rules with the /cleanclientrules or /cleanserverrules switches.

4. /restore. Similar to safe mode, the /restore switch attempts to open Outlook in the last-known clean configuration. If Outlook has shut down without reason, this switch attempts to open Outlook with the last set of folders that worked. Using this switch in conjunction with safe mode can help restore a crashed Outlook back to full functionality.

5. /cleanautocompletecache. In previous versions of Outlook, the .nk2 file was responsible for auto-completing email addresses. It was only visible when Outlook is off and is stored within the users’ profile. Outlook 2010 no longer uses the .nk2 file, but instead adds an additional category to your Outlook contacts, called “suggested” contacts. The .nk2 file still exists -- although it is no longer called .nk2. It is stored in the user’s profile at: C:\users\%username%\Appdata\Local\Microsoft\Outlook\RoamCache\Stream_Autocomplete*.dat.

However, unlike the old .nk2 file, deleting this file will not remove cached entries. This is where the /cleanautocompletecache switch is useful. It lets you clear out the suggested contacts cache and start anew.

You can also clear the cache using from the Outlook options. Simply navigate to Mail tab -> Send Messages -> Empty auto-complete list.

Dave Leaver has worked in the IT industry for the last ten years as an IT support engineer. He currently works for an IT support company in Cheltenham, UK, supporting over one thousand users, spanning over forty companies. Leaver specializes in Microsoft system migrations and Exchange Server. Leaver has also been a network administrator for the NHS and several large construction companies throughout the UK.

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