Outlook has a nice feature, you can assign a web URL to a folder. So in a nutshell you don't have to leave Outlook and start a browser to access the archive.

Prerequisite: have a working web interface of piler

Configuring Outlook to access the archive

1. Make a new folder, eg. “EmailArchive”
2. Right click on it, then select “Properties”, and the “Home Page” tab.
3. Select or check the “Show home page by default for this folder” cehckbox
4. Enter the URL of the piler gui, eg. http://archive.yourdomain.com/
5. Click on the “OK” button.

Screenshot: accessing the demo site from Outlook 2013

Note that it's best if you configure single sign-on, so you can spare your users typing their credentials to piler.