'Content-Transfer-Encoding：7bit'

I have a problem here. I created a mail() PHP script to send attachments and you would normally send in your regular email provider. The problem is that I can only send files up to a certain number of characters. For example I can send a file with this name "New Text Document" but if I try to send a file with this name "New Document of Microsoft Word (3)" it never gets to my email.

Can someone please tell me why this happens?

Here's the code http://pastebin.com/5PShDq5P