Go to singpost (Singapore National Post)! Choose to deliver by hand! This certificate will arrive at the destination in 3 days by express delivery! You should first record the address you want to mail and the detailed information of the recipient, go to any SINGPOST post office, tell the staff that what you want to check is Unfolded and Urgent, ask her what to do, and they will help you fix it and collect the money OK~~
This post office courier company is a national company in Singapore, which can check the mail receiving status and track the mail location.
I sent my diploma, degree certificate and pass by express mail at Singpost, and I didn't lose any of them, and none of them lasted more than 3 days. But you should avoid sending it on weekends, because usually this courier company doesn't deliver it on Sundays. . .