well, since the mail file is a simple text file, you could always VI it, but good luck getting that into memory
I don't use sendmail, but postfix with Maildir format. However, if you post a sampling of the mail file, enough to cover 3 or 4 emails, (with private data removed, of course), it may not be too difficult to throw together a perl/python script that will strip away the ones you don't want. Or, you could look on the web to see if a tool already exists.
davidj