We do something similar on our wordpress site, using zapier. When people download a file from our resource library, add their organization or sign up in the community, an email is sent to zapier which then adds new contacts, organizations or website actions. We can then follow up via salesforce.
Since zapier just uses the API of salesforce, it should be possible for a programmer to do the same without zapier. But using zapier is a good quick and dirty solution too, perhaps using a dedicated subscribed user who is notified by email by discourse or something like that.
That said, salesforce is complex and hard to use for us, and we’ve had some issues with zapier imported data not being reliable, so we’ve been devoting our time ad energy instead towards moving our workflow out of salesforce and other tools and into discourse. Discourse is central to my community, so my approach is to try to instead contribute to improving discourse functionality that makes this possible, like group inboxes, tagging personal messages, staged users and the like.
More on that over here: