Error message - Mail appeared to be SPAM or forged

­ Suppose someone wants to send you an email to your mailbox address. It may happen that the email does not reach you, but instead the sender always receives the following error message:

Remote host said: 550 : Recipient address rejected: Mail appeared to be SPAM or forged. Ask your Mail/DNS administrator to correct HELO and DNS MX settings or to get removed from DNSBLs;

The problem here lies in the configuration of the mail server that delivers the email to us. We check its DNS name using its IP address. We also check the value it passes to our server as ‘HELO’ - as defined for the Simple Mail Transfer Protocol (SMTP). If these two do not match, we reject the email. And for good reason: a difference between DNS and HELO names often occurs on servers that are misused for sending spam emails.

According to [RFC 2821] (https://www.ietf.org/rfc/rfc2821.txt) (the current definition of the SMT protocol), the ‘HELO’ is used to identify the client (i.e. the mail server that wants to send an email to our server) and should therefore correspond to its "[Reverse DNS Lookup] (https://en.wikipedia.org/wiki/Reverse_DNS_lookup)" (in which the domain name stored in the DNS is determined inversely from the IP address).

In situations where the client cannot specify a meaningful HELO (e.g. due to a dynamic IP address), RFC 2821 recommends using the IP address in the HELO instead.

Cause of the error message

The client is probably simply specifying the sender domain of the email as HELO instead of its own host name. Although this is not prohibited, it is neither a sensible configuration nor does it comply with the SHOULD requirements of RFC 2821.

Solution to the problem

The sender of the email that did not reach you must contact their email provider (and ask them, for example, to use HELO in accordance with the standard). Neither you nor we can resolve this issue.