You can email into any folder with an "email" alias or by emailing to the DBID which is less helpful.
See the wiki for details on how to add an email alias. (Although I think the doc will use Explorer rather than Share)
There's an enhancement request open to automatically add email alias to share sites but its not yet considered or implemented.
In addition as mentioned above its possible to add email handlers to process inbound messages so for example emails could become comments on a document or whatever is appropriate to your requirements.