Can not receive emails on the server – Directadmin


in my Directadmin VPS emails Send correctly but I can not receive emails from Gmails,

Using the Cloudflare system to control domain and DNS records,

site parked in, example:, for example from IP:

Now I got to the point of the main domain of cloudflare: One record: >> —- and Mail: One record >>

and MX records set: MX handled by,

now on VPS can not receive any email,

When the email is sent to these points (for example,, this error message appears and is not delivered:

The response of the remote server was:
550 authentication required

What a problem? How can we know and fix this? How can I and what site or tools exist that can test my records or can they send error messages to the system?