Before Installing the SP1 Windows Download Make a restore Point Just incase.
Go to your C-Drive and go to the Program folder which in put the Windows Mail folder which you got from your old vista OS. Copy and save it to a thumb drive and also you can save it to your desktop. After that DELETE it from your programs folder. If it won't let you delete it, you must take OWNER SHIP of the file, I will put the Reg file on here so you can downlaod it. Go ahead and download and install the SP1 from MS. After install you will get a pop up saying Windows mail MSOE.DLL is missing, just click ok. Go Back into the program folder, you will see that SP1 put a new windows mail folder in there, DELETE IT. Then paste your old windows mail back in there, The one from VISTA . Your mail should work again just like before.
If this worked for you please reply, If you need the windows mail file folder let me know and if you need 32 or 64 Bit
If you install SP1 already you should have a restore point from MS they put in, and also if you have a copy of the Windows mail folder from Vista remove the one SP1 put in there and replace it with the Vista one. See if that works before restoring. Take Ownership Shortcut