If you are using Gmail, did you set up POP correctly in the Gmail settings?

I send attachments on a regular basis using Gmail, and even Hotmail (don't hate me, i'm trying to get away from it).
The difference being, I don't bother with the using Gmail as pop/smtp, I just do it from the web interface. Same goes for hotmail. No real need to pop/smtp if webmail works.
I know of no 'special' thing you must do to send attachments....., but if you're getting some type of errors, tell us about them.