Someone in the house (ahem, the mother) doesn't really understand sending 500 emails of 'funny clips' kinda kills the cap. Is there any way I can limit the send/receive sizes? She uses Outlook Express.
I don't think Outlook Express supports setting a maximum attachment size. This is normally a function of the ISP's mail server that has a max size limit, which in your case is far higher than you are wanting.
Maybe you can look at installing some sort of smtp relay service on her computer, so that her client delivers mail to 127.0.0.1, to a relay service, which you then configure max size on and that inturn delivers to your ISP.