attachments through mails

Question

does attachments through mails being sent from windows forms reach receipents? bcos i tried sending a small text file through one mail id of mine to another but only messsage is going. i tried sending from gmail to yahoomail and also vice versa but only message is being delivered. is it only possible in web apllication or does it work even in windows application as well. just i need a clarification and also how does it work? some explanation if i get so that i understand the process. I would be really greatfull.

Thanks in advance,

Avinash