I can't connect my email to my email client

Hi all, i have a server on RackNerd, after I successfully installed Cyberpanel, and my website was online, I created an email on Cyberpanel. Then I connected via my email client (MailBird) but it was always rejected, I have entered the data correctly, such as “Server Hostname”, “username” and “password” for my email… What should I do?

Email system is not stable now