Here is some information on how the outlook clients connect to the public folder information store to download the oab messages/attachments.

For an outlook client to download the OAB files the client has to make a call in to the address book provider, which searches the public folder tree and returns a list of the OAB containers available.  If there is more than one container available, the client must choose one to connect too.  If the container chosen is a later version of the OAB container (OAB Version 2, OAB Version 3a and OAB Version 4) currently on the user’s machine (client profile version), then the client must also choose whether to do a Full or Incremental download. 

Full OAB Download: The address book provider (EMSABP) opens the current OAB message.  It first selects the template file that matches its own locale ID and code page, it will save it to disk, uncompresses the message and then renames it to TMPLTS.OAB in the Windows directory.  The client will then pull down each of the four data file attachments, uncompress them and then saves them in the Windows directory as well.

Incremental download: The address book provider (EMSABP) searches for the Diff message whose sequence number matches the value of the client’s current OAB, saved in the MAPI profile in the registry. The client will then pull off the attached Diff file, uncompress it and then merge it into the previous OAB on disk. The client will repeate this process until the sequence number matches that of the current message, indicating that the client’s OAB is up to date.

As mentioned in my previous blog the client side files can be found at the following location: C:\Documents and Settings\UserName\Local Settings\Application Data\Microsoft\Outlook