Blocked But Not Blacklisted

I have two MIAB servers on two different hosting companies. One works perfect all the time. The other ( however, has recently started kicking back emails the following errors:[] said: 554 5.7.1 Service
unavailable; Client host [] blocked using (in
reply to RCPT TO command)

But nothing is black listed at spamhaus.

Also, sometimes, when I try to send from the emails address i get:
SMTP Error (554): Failed to add recipient “” (5.7.1 Service unavailable; Sender address [] blocked using; Error: open resolver; DNSBL Error Code - Open/public resolver - The Spamhaus Project).

Also, I get block notices for various domains on my server but their not blacklisted at spamhaus.
This domain is listed in the Spamhaus Domain Block List (code, which may prevent recipients from receiving your mail. See and

I’m at a loss to understand why this is occurring. Sometimes, when i reboot the the errors will clear both ways, only to come back a few minutes/hours later. Neither of these server are heavy traffic and both resolve to themselves as far as DNS. Any help anyone can provide will be greatly appreciated!

This doesn’t appear to be a configuration issue and since it is intermittent it is difficult to troubleshoot.

Unless someone who has experienced exactly this problem can help you, the only option I can see is to disable Spamhaus checks in /etc/postfix/, possibly start with just the sending check (it is there twice, and I think one is only checking sending).

Note this will be disabled for the entire server and is an unsupported modifications, so whenever you update MiaB or even just run sudo mailinabox, the MiaB scripts will revert the modification.

Thank you for your reply. I ended up moving servers to a different hosting company. Seems that my original host was doing some “funny business” (<- technical term) with there networking. Something wired with their DNS. I don’t claim to fully understand, but after moving hosting companies, everything is back to normal. Thanks for your assistance.