First don't get over excited as the hack I'm gonna explain is for Storing the E-Mails which are Synchronized from your PC' Outlook via ASync and not those directly downloaded via POP3 accounts in Pocket PC. Anyway this is of very helpfull as it saves lot of those precious little memory. 

 Well, its just a simple Registry Hack away,

1. Create a folder in your Storage card, for storing the mails. I used Storage card\Mails
2. Add the String PropertyPath under HKCU\Software\Microsoft\MAPI
3. Enter the above path for mail folder in the Value field
4. Soft-reset your device.

As you may know that the Today plug-ins load even before the Storage card gets the juice of power, it clashes with the hack and so you may need to Disable the Messaging Today Plug-in if it reverts back.

I will add this hack to Registry tweaker PRO . Those who have already purchased, enjoy with free upgrade!