PaveNess
Sounds like your MX/AAAA/A DNS records are borked or maybe your server's DNS is borked. It basically means you have the Verify Email Addresses setting enabled (Admin Panel > Emails > Settings) and your server is unable to locate the proper DNS records for the email address you are attempting to use so it fails the verification check. You can disable the setting until you figure out your DNS issues on the server.
Cheers.