Emoticons And E-Mail

I have emoticons saved in a folder to use in e-mails (emoticons like those and similar to the ones used at MG when typing a post or reply).
For example;
The smiley face.


My internet service provider is with "Sympatico". When I create an e-mail with emoticons inserted into it, and send to a friend who is with "Cogeco", we both can see the emoticons in all the replies when sent back and forth. It stays the same as created.

However, when I send the same e-mail to a friend who has Hotmail, and I receive their reply, my emoticons are replaced with the file name I've given to it (for example, "smilie emoticon") in their replies, instead of the actual emoticon themselves. The filename is written in text in place of the emoticon, the text is written as well at the very bottom of the e-mail.

Why is it that emoticons in one e-mail stays the same, and the other is replaced with text (filename) when originally sent with an emoticon?

Know what I mean?
Thanks!