We were facing an intermittent issue with the Spam engine across all our Inbound Mail servers. Due to which, mails sent to the domains hosted on our mail server were rejected with following bounce back:
The mail system
<emailaccount@yourdomain>: host mx3.mailhostbox.com[184.108.40.206] said:
Service unavailable; Helo command [ob3-1.mailhostbox.com] blocked using
dbl.zen.dlls-tx.mailrbl.com; v=spf1 a -all 554 5.7.1 Please see
for explanation of the problem. (in reply to RCPT TO command)
This issue has been fixed and we are putting this post for your perusal.
Please feel free to contact our support helpdesk in case you have any queries.