Longer answer:
Printing is typically done by preparing a document (HTML, PDF, Excel...) and sending it to the client, which in turn sends it to a local printer. If your server is on a local network (physically or logically, i.e. connected through some form of VPN tunnel) it would be trivial to add some code which could send the attachment from the server to a printer, but then... Attachments are not necessarily printable. They could be anything - binary files, sound recordings etc. Even something as seemingly "printable" as a word processor document is really only printable through the application which created it.