Hi @doruku. Thanks for being part of GoDaddy Community! The first thing to look at is whether or not any of the messages that aren't getting through have something in common, like the from address, content, or subject. Another thing to look at is whether or not the messages receive a rejection notice. That will usually have some clue as to why the message was rejected. If you're not able to determine an issue, you can also contact our support team. It is possible for our advanced support team to look at the mail logs to see if messages were rejected from our end.
JesseW - GoDaddy | Community Manager | 24/7 support available at x.co/247support | Remember to choose a solution and give kudos.