You may face this error called ‘550: relay not permitted’ if your remote email server is misconfigured on your web / email hosting service. You may even face this issue when you have misconfigured your DNS settings on your Cloudflare account.
Main symptom is you are unable to receive emails on your email id.
So how to fix this?
Solution is simple!
There are two records needed to correctly point your Email Hosting Service Provider. A ‘MX’ record and an ‘A’ record. A MX-record points to the mail.yourdomain.com domain and the A-record for said domain points to the right IP address provided by your email service provider e.g 220.21.22.234
Note: For example I am using Cloudflare’s DNS settings to correctly point to right Email Hosting Service Provider.
‘MX’ Record ‘10′ ‘mail.yourdomain.com’

‘A’ Record ‘mail’ ‘220.21.22.234’

I hope this informations helps you to solve ‘550: relay not permitted’ error in your mail server settings
Thanks & Regards
Mandar Apte