You can send or forward any email to message+SUBDOMAIN@crmondemand.biz and create a message. If you want to associate it to a particular lead, opportunity, customer or archive, just type in part of the person's name (substituting spaces with a "_"). Heap can even auto associate the message based on the "to" and "from" addresses if you choose not to specify the association explicitly.

Your subdomain is the first part (before the first period) of the web address you use to login to your Heap account. So, for instance, the company above would sign in to their Heap account at http://creativearc.crmondemand.biz/. Thus their subdomain would be creativearc.