For the love of all that is holy, when people offer you their email addresses, take them! Don't look for alternate ways to engage prospects long term. Get email right, right now.

There's a reason email drip marketing is such a hot topic in startupland right now. It turns out that email is a pretty damned effective way to stay engaged with people, especially compared to "hoping someone subscribes to this RSS feed or ever remembers to look at this website again". Don't make your prospects remember things; do the remembering for them.

Try using Mailgun instead of an actual email server you run; we've had a lot of good luck with it.