After configuring the SpamExperts email filtering service, emails may bounce with an error message similar to:
550-Please turn on SMTP Authentication in your mail client, or login to the 550-IMAP/POP3 server before sending your message. mx48.antispamcloud.com 550-[18.104.22.168]:54550 is not permitted to relay through this server 550 without authentication.
To resolve this, make sure that after changing the MX records the Mail Exchanger in cPanel is set to Local Mail Exchanger:
If you still getting errors, please consult this giude