A Classic Utility for Reducing Mailbox Size Still Works in Outlook 2007

Many years ago Ewan Dalton, a Microsoft employee from the UK, created a nifty tool designed to trim unnecessary messages from ongoing conversations. (His blog is found at blogs.technet.com/ewan/.) This tool, a COM add-in, is called Thread Compressor. Evan Morris wrote an article about it seven years ago called Using Thread Compressor, May 2002,InstantDoc ID 25119. Though it was originally created for Microsoft Office Outlook 2000, Thread Compressor still works for all subsequent Outlook releases so far: 2002, 2003, and 2007.

Thread Compressor works on a variety of Windows clients including Windows 2000, Windows XP, and Windows Vista, both 32- and 64-bit. Because much of Thread Compressor was written in Visual Basic 6, it’s not managed code and it doesn’t require the .NET Framework. Collaboration Data Objects (CDO) 1.2.1 is a prerequisite. CDO 1.2.1 isn’t part of the Office Outlook 2007 installation, so you need to download it from here www.microsoft.com/downloads. The .exe download is a self-extracting archive with ExchangeCdo.MSI, which when launched will run the CDO 1.2.1 Installation Wizard.

Thread Compressor is available for download from the recently created domain threadcompressor.co.uk. Extract the zip file download to an accessible location on the client workstation, such as c:program filesthreadcompressor. The Thread Compressor application isn’t bound with a Windows Installer; you’ll need to register some ActiveX Controls with the .ocx extension and a .dll manually from the command line as an administrator. On Windows Vista, if you’re not logged in as an administrator, you can open a command prompt with the Run As Administrator option.

From the command prompt, run the regsvr32 command from the extracted folder location for each of the four files as follows:

>regsvr32 comdlg32.ocx

>regsvr32 msflxgrd.ocx

>regsvr32 tabctl32.ocx

>regsvr32 threadc4.dll

The order doesn’t matter. For each one, you should get a pop-up message advising of a successful registration as shown in Figure 1. For more information on how to use regsvr32.exe, see the Microsoft article Explanation of Regsvr32 usage and error messages.

You install Thread Compressor by loading the COM Add-in within Outlook 2007, if it’s not already there. Open the Trust Center in Outlook 2007 by clicking Tools, Trust Center. When you select the Add-ins button on the left bar you should see the Thread Compressor add-in in the right pane; it’s highlighted in Figure 2. To verify that this add-in is enabled, ensure COM Add-ins is selected in the drop-down box at the bottom of the page beside Manage and then click Go. This opens the list of Add-ins so you can see which are loaded. If the check box isn’t selected beside Thread Compressor in the list, select it, and click OK. Figure 3 shows Thread Compressor listed among other Add-ins. Now the option to Compress Threads should be present at the bottom of the Tools menu in Outlook.

The first time I ran Thread Compressor its interface didn't open, and it appeared to install Outlook 2007. I had to close Outlook 2007 and restart it (that is close the application, not kill the outlook.exe process). After opening Outlook again, the Thread Compressor functioned as expected. When selecting Compress Threads from the Tools Menu, the Thread Compressor window opened as shown in Figure 4.

You can use the Thread Compressor window to apply two types of whitelisting before you run the application. You can exempt deletions based on message attachment type or sender. I chose to have Thread Compressor ignore messages with the file type .pdf; Figure 4, shows this choice. You can also add the SMTP address of senders whose messages you don’t want deleted using the Exceptions button. I also selected the box instructing Thread Compressor to use the Deleted Items folder for the purged content. Without selecting that box, the superfluous content is given a hard delete. Moving the messages to the deleted items folder at least the first few times you run the application allows you to easily peruse the messages prior to permanent deletion. Click the Thread Compressor Windows Options tab to see four settings for logging each run—None, Low, High, or Debug. You have the option to rename the log or append to a previous log. When the log is set to High, it records the messages it deletes with Sender, Subject and MessageID logged.

Use the Thread Compressor Advanced tab to control whether Thread Compressor ignores some messages with certain properties such as Read Receipts or messages marked with High Priority. Thread Compressor can be run against any type of Outlook email account, including POP3, IMAP, and Exchange Server. Thread Compressor deems messages to be unnecessary if they have already been replied to within a conversation thread. Thread Compressor is even able to make this assessment for IMAP messages with just the header downloaded. Thread Compressor removes messages that have been replied to within an email conversation. Messages within a thread that haven’t been replied to will remain in their folder. This reduces the number of messages in the folder, leaving only content that has not yet been responded to.

In my test I ran Thread Compressor against three Outlook accounts. Each account had a balance of list subscriptions with other emails. Thread Compressor removed about 10% of the content in each case. Figure 5 shows Thread Compressor in action. Figure 6 summarizes the amount of data that would be removed for one of my accounts with 401MB of email data.

The value of this tool really depends on your users’ specific email usage patterns and your corporate messaging policies. If users participate in lots of multi-recipient conversations, they’ll probably see the greatest reduction of content in email folders. It’s great that a software tool can still be useful even though the application it enhances has gone through three major upgrades. Ewan may be coming out with a version 5 of Thread Compressor. If so, I hope it will work on Outlook 2010, because there doesn’t seem to be an end to information data overload.