Diagnostic-Code: smtp; 521 5.3.0 Upstream error, please check

Hi. I try connect my hosting provider mail server with Cloudflare.
I recieve error when send message:

Action: failed
Status: 5.3.0

Diagnostic-Code: smtp; 521 5.3.0 Upstream error, please check for possible
reasons why. SLJQ3syMb2We

Welcome to the Cloudflare Community. :orange:

You mention that you have a mail server with you hosting provider, but your error is from Cloudflare Email Routing which you would normally use if you didn’t already have domain email. If your existing mail server has mailboxes for your domain email, you will want to use an MX record to direct your email to it rather than Cloudflare Email Routing,
which is simply a forwarding service.

If you would like more specific answers from the Community, we will need to know your domain name.

1 Like

My domain is lytkins ru

That error message appears to be from the recipient mailserver. You will need to determine why it is sending a status code that suggests it does not receive email. Are you able to obtain support from the server operator?

So far I have not been able to get support from my hosting provider. MX records are configured on the side of my DNS registrar.

You have removed the Cloudflare Email Routing. That’s a step un the right direction if the new MX host is configured for your domain mail. You will need to engage the host of you are having delivery issues.

My provider says: “ The essence of mail forwarding is that letters to the addresses of mail servers in the domain MX records are received on Cloudflare and then routed according to the specified rules.

This service is supplied by Cloudflare and you need to contact them to clarify the procedure for setting up mail routing and questions about additional settings.

To delegate mail to our mail servers, it is necessary to use the addresses of our mail servers, in the domain MX records or as final hosts when proxying.”

I’m looking for a solution where I can protect my domain using Cloudflare technology. In terms of DNS protection, everything worked out. It came through the post office. My hosting provider requires MX records pointing to its servers. As I understand it, Cloudflare cannot work in this mode? What kind of compromise is possible in this case?

I don’t know what you mean by that. Most domains with email that use Cloudflare DNS use MX records that point directly to their mailserver and not Cloudflare Email Routing. If you have configured your MX records so that your mail is sent to your mailserver, that should be all you need to do to at Cloudflare to set up your inbound mail.

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