Hey there, @RianneS 
Thanks for reaching out, and welcome to the Netlify Forums! Sorry to hear that you are having trouble getting your form notifications to work.
This Support Guide is the first port of call to debug any forms issues. Have you read through this yet? There are also many other Support Guides for forms - you can find them here: #Netlify-support:support-guides
We also recommend trying to search the forums or look at topics tagged Netlify forms if you haven’t already - it’s likely your question was already asked by someone else! In your case, it looks like there is a related thread here of folks who had this issue, most of which were caused by a hard bounce.
In order for us to look into your specific case further, we will need a link to your Netlify site, your form name, and the email address this is not working for.