Filter to send Mails with "funny" attachments later

Hi.

Due to the upload limitation of our inet conncetion,
sometimes the upload is "blocked" by mails with big
attachements like funny videos, .pps or large images.

To use my ssh connects to servers outside the LAN
i already set up some qos rules on the router.
Also for dns queries.

Complete blocking of this attachements is easy,
but i want to check for the attached type and
send this messages later (after working time).

Does anyone know howto do this?

chris