hey thx. i completly forgot about the registry... a quick search and i found a key which im assuming is the currect one....
Code:
HKCU\Software\Microsoft\Inbox\SMSText\
DWORD : MaxDeletedMsgs
VALUE : 50 (Dec)
which i then changed to 65535 (which i believe is the limit for a 16bit unsigned integer...) now ill just wait and see when it gets past 50...