All incoming emails have stopped and using Spamhaus? Here is why! All incoming emails have ...

All incoming emails have stopped and using Spamhaus? Here is why!


Our support staff ran across multiple support tickets where email store/forward users suddenly stopped receiving emails from us and it turned out to be their server's configuration issue with Spamhaus who is preventing access to their free blocklists using a public DNS.

Our store/forward service receives emails for users who cannot receive emails on standard SMTP port 25 and then forwards the emails to their email server on non-standard ports such as 2525, 26, 587, etc. Other users may also use the store/forward service to run their emails through our spam filter system. The problem happens when they also use Spamhaus on their own mail server and Spamhaus blocked their access. The error message Spamhaus returned was also misleading so the users cannot identify the issue without digging deeper into it. Below is the error that our server has received when delivering emails to the email store/forward user's server.

550-Rejected because is in a black list at
550 Error: open resolver;

Note that our mail server IP is not on any blacklist and the real reason is that Spamhaus blocked access to their free blocklists from the user's server. Details of the error can be located at
Spamhaus DQS
According to Spamhaus, to successfully query Spamhaus via public/open resolvers, The users need to sign up for the free Spamhaus Data Query Service and make the relevant change to the server configuration.

September 14, 2022 AT 03:03

thank you for sharing


Sami AlRiyami
October 23, 2022 AT 09:43

Why email server rejecting the incoming mails?


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