My outlook quite often can't receive mail in traditional chinese. What is see is alot of ?????

I bought a Dell latitude in Singapore in March 2007 and I am now working in Taiwan. I am using the first batch of Windows Vista. I use Outlook for my mail. Whenever I received mails in traditional chinese, most of the time, I only see lots of???? Despite using the encoding to change it, it doesn't help. I don't know what exactly is the problem. I hope someone can enlighten me on this.