Allow users to email a file and create a new post
You have two options. The less efficient (but easier) way is to keep it in Drupal

The more efficient (and more difficult) way is to do a bit of this outside Drupal and hack at your MTA and/or use something like Amavis to do it.

Since you're on a Drupal site, I'll give you a quick rundown of how I might do this if I had to keep it in Drupal.

What you need to do is have the random generated email checked by Drupal regularly.

Create a module that periodically (via cron) logs in to each user's associated email address (these should be IMAP accounts!).  If it finds a message that has the right subject line to trigger a new content post, then download the attachment and save it to the file system.  

Keep in mind, this could be a crazy thing to do if you're dealing with a lot of users.  The better option would be to have the emails processed outside of Drupal, and then use something else to trigger the Drupal content creation.

No matter which way you go, you're looking at quite a bit of programming. I have never seen a module that does this.