I am unable to email an email address I’ve got set up, it bounces with a 550 error. I contacted my hosting provider, they suggested it has something to do with me having my domain on Cloudflare
said: 550-Please turn on SMTP Authentication in your mail client.
550-mailout-l3b-97.contactoffice.com [22.214.171.124]:55300 is not permitted
to 550 relay through this server without authentication. (in reply to RCPT