Port 38870 used by MAPI-PREOP Application - Possible Spam?

I've googled on this to no avail so am hoping that someone else here may have seen this.  

In checking my network traffic connections just now I came across a situation where a workstation at one of our remote sites is connecting to the server across port 38870 via the application MAPI-PREOP.  I'm not finding much information online about this port and am concerned that I may have a possible security issue.  The workstation is XP pro SP2 with the latest updates and McAfee virus catalog.   The server is SBS 2003, also with the latest updates.  

Please advise.   I could just block this port to see what breaks but would prefer to know in advance what it might impact.  
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jeniehAuthor Commented:
Ok, in looking into it further one of our WAN Accellelleration devices creates this as a Mapi caching item so that users can load their email faster.   I'll request to have the question closed.  
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