Welcome to the forums @AlexH
Without knowing the domain it is hard to check things and give definitive answers, however…
Reading your post I believe you are now using Netlify DNS for the domain, meaning you have set the nameservers to those specified by Netlify (e.g. dns1.p02.nsone.net). Is this correct?
You might find [Support Guide] How do I migrate a domain to Netlify DNS with zero downtime? and also [Support Guide] How can I receive emails on my domain? provide very relevant information in this case.
If you have further questions do not hesitate to reply.