How do I create attachments with sendmail?
You don’t. Sendmail is a mail transfer agent (MTA). Creating e-mail messages, including adding attachments or signatures, is the function of a mail user agent (MUA). Some popular MUAs include mutt, elm, exmh, Netscape, Eudora and Pine. Some specialized packages (metamail, some Perl modules, etc.) can also be used to create messages with attachments.