Use https://maddy.email, it's fantastic and will spit out DKIM for you. The rest (DMARC, SPF) you'll have to set up yourself but it's mostly setting up DNS records.

Is there a reason why you're not choosing an email provider? there are very cheap ones out there. What you're trying to do is normally called "transactional" email normally and there are a lot of providers who specialize in that.