WebMailPRO and MessageGuard both export mail as EML files. These files can be opened in lots of different viewers, including Mozilla Thunderbird, Microsoft Outlook Express, and SeaMonkey. Recent versions of Windows Explorer allow you to view and search the EML files while they are still in the compressed .zip archives that WebMailPRO and MessageGuard provide for download.
These instructions show you what needs to be done to open EML files in Microsoft Outlook 2003 & 2007. Microsoft Outlook 2010 supports EML files natively, so you do not need to perform these steps.
Microsoft Outlook 2003 & Microsoft Outlook 2007.
Before you can perform this tweak, you must be using the latest versions of Outlook 2003 or Outlook 2007. This means having the latest service packs installed and all the patches.
The link below will take you to a page to download a zip file with 4 ".reg" files in it:
These registry files add registry keys and values to your system to associate EML files with Outlook, and run Outlook with the appropriate swithces when double-clicking on an EML file.
As an Administrator on the computer, extract the zip file, and simply double click / run the reg file that matches your version of Outlook and your Windows environment (32 bit or 64 bit). If you installed Outlook to a different path then the default, you'll have to edit the reg file to change the path to Outlook.
To download the zip file, go to http://kb.k12usa.com/Downloads/Outlook-2003-2007-EML-Patch
3rd Party Utilities
Here is a list of Utilities that can help with the import of EML files to an Outlook PST file.