Setup an instant post notification on categories

Hey all,

I need some advice. My website will have no users, nobody can register on my website as a user. At least that was my plan. I want visitors to be able to subscribe to categories though. And for this I was looking into MailChimp using groups. I want subscribers to immediately receive an e-mail after I make a new post in a category they subscribe to. For now I will not send them a weekly newsletter, but I want to be able to in the future.

With RSS to Email from MailChimp you can only set it to send once a day and not straight away after a post. So I found the AutoChimp plugin which would do exactly what I want it to, but it’s old and not updated anymore. So I don’t think that’s a good idea.

What would you advise me to do? Maybe do let people register on the website and use a plugin that does the trick? Is there an alternative to Mailchimp preferaly also free until a certain number of users? I’m open to anything that would work, although I can’t commit myself to something with a hefty monthly fee yet.