Why don't users receive the verification mail after registering at my website 'osclass'?

I am sure you'll work it out - just use common sense and you'll find the solution :)

You don't give us much to work with, but I'll give you a couple of suggestions. Is it failing for everyone? Or do some people get their verification mail? Look for a pattern, is it common to one email provider and not to another? For example: Do Yahoo mail users never get the verification? And do Gmail users always get it? Do you instruct subscribers to "White List" the address that you are mailing from? And to be sure to check their "Spam" folder for the verification mail? I see many email