First and foremost, congratulation and good luck.

You sorely need a free tier, with limited emails or less features (say for example, no referrals).

This is the second try of this kind I see on HN and I think there definitely is a market space to fill for this kind of service. But for something so simple (many people just use the free tier of mailchimp to set up a basic subscription form) you probably need to invest massively into a free tier to get the word of mouth out.

Also: a live demo would be nice.