Email Delivery Issues - DNS Configuration, Mailbox Unavailability

We’re experiencing multiple email delivery issues and are receiving multiple emails daily, including mailbox unavailability and DNS configuration issues, and we need to find a solution to minimise the impact of email delivery to our customers.

Error messages include:

  • Address not found. The response from the remote server was: 550 No Such User Here.
  • Address not found. The response was: DNS Error: DNS type ‘mx’ lookup of mailknox.com responded with code SERVFAIL
  • Address not found. The response from the remote server was: 550 Requested action not taken: mailbox unavailable.
  • Address not found. The response from the remote server was: 550 5.5.0 Requested action not taken: mailbox unavailable (S2017062302).

We’ve been informed by Google to contact our domain hosting team for support!

Hoping others with similar issues can shed some light on how they tackled this or if there is a way to fix these issues.

And you receive these errors when you send emails?

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Is the mailknox.com domain yours?

The current set up for the mailknox.com domain is currently containing multiple mistakes, that are all leading to unavailability, delivery issues, and so on, such as for example:

  1. Using Mail-in-a-Box, and their bad (default) configuration(s).

  2. Operating with one single name server, which is in violation of the Internet Standard RFC 2182 / BCP-16.

  3. That one single name server does NOT respond to any DNS queries, from anywhere in the world, which means that the mailknox.com domain is completely unavailable, due to #2

The above domain doesn’t use Cloudflare though, so I’m wondering:

How exactly does Cloudflare come in to the picture here?

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