'Sharing' personal folders without using Exchange?

[the.damon]

We use an externally managed exchange account for our main email and dont have a great deal of space allocated to it. Due to this, we have a PST which is used to archive the sent & received.

 

Is there any way I can share the PST (or setup an alternative) so that multiple users on our network can access it at the same time?

 

We would prefer not to go the whole hog and install our own exchange server so if anyone has any knowledge of workarounds or 3rd party applications (will throw money at it if needs be) it would be much appreciated.