This only deals with storage of the file. Your SMTP-server still has to deal with every email and every file, and your mail server still has to receive every o

This only deals with storage of the file. Your SMTP-server still has to deal with every email and every file, and your mail server still has to receive every one of those before it could even start to consider deduping. This is probably what's murdering your email system. Quickest solution for your problem would be to put the file on a share accessible for all recepients and just link to it from the email text.