No, a lot of times, the attachment is more important than the text of the e-mail.
But anyone who tries to auto-delete my attachments will never get my patronage.
Why do you want to cripple email to create a free service? This seems like a race to the bottom, with very little upside for you.
Limiting attachments - the only possible way for free ADs-based alternative.
Mail search - will be offered. But old emails w/o attachments.