I want to add a new customer to our Magento store, but am rejected to save it due to the email domain of that customer's email address info@[domain].zone. I couldn't reproduce the problem in a teststore we are having, so it may be a sepcific issue

I can't post the exact error message but it seems Magento doesn't know about the .zone domain and I was wondering where I can add it to something like "acceptable mail domains" in the magento backend?

disclaimer: I'm fairly new to Magento and likewise may miss some of the basics yet. Sorry if I may use incorrect terms (which is also due to little experience)