Partial e-mail body receiving by SMTP Server?

I would like to setup a SMTP server for processing of e-mails (my SMTP server). E-mails will be forwarded from well know Internet e-mail servers to my SMTP server, but the only fragment of body is important for processing (like first 10kB of e-mail, not attachments just text). The rest of the transferred e-mail, should be discarded during