DNS Blacklist Monitor

This tool helps maintain a current black-list of spam sources.

DNS blacklists monitor software monitors your email server public IP address in DNS blacklist zones like zen.spamhaus.org and others. DNS blacklists monitor software continuously checks if your public IP address is listed in any DNS blacklist and if public IP address of email server has been accidentally registered in any DNS blacklist zone. Blacklist monitor software lets e-mail system administrators know if there is a problem in outbound e-mail messages. DNS blacklists monitor software will send a notification to the administrator to take action about this issue and minimize down time for outbound email messages. If your public IP address does get blacklisted, your users will not be able to send out mail freely. Unless the administrators get to know that, their IP is blacklisted, action will get initiated only when users complain of the problem. You tend to lose quite a bit of time.

As soon as the monitor provides a warning, the administrators can start to resolve the problem. In case of a problem, you will be notified by email, SMS or both with all needed information to begin troubleshooting immediately. Blacklisted IP address, blacklist zone and removal URL address, etc. are made available. You would be able to pause outbound email messages and remove IP address from DNS blacklist zone. Only thing to be done after that is to wait for DNS replication for about an hour. Sending out of email messages then can resume. The administrators should find out the reason for getting blacklisted, so that you do not get blacklisted repeatedly. The tool checks the status every half an hour. This is a very good tool.

DNS blacklist (DNSBL) monitor software is used to monitor your email server public IP address in DNS blacklist zones like zen.spamhaus.org and many others.
Why you should use DNS blacklist monitor software
Blacklist monitor software lets e-mail system administrators know before users told them that there is a problem in outbound e-mail messages because DNS blacklist monitor software continuously checks if your public IP address is listed in any DNS blacklist and if public IP address of email server has been accidentally registered in any DNS blacklist zone, DNS blacklist monitor software will send a notification to the administrator to take action about this issue and minimize down time for outbound email messages.
Of course some outbound messages may be rejected by recipients which depends on what DNS blacklists used by recipients Anti-Spam and time taken to resolve the issue.
The below flow chart show how your outbound email messages will be checked for spam on the recipient email server side (Image from spamhaus).
Why getting blacklisted in DNS blacklist zone is dangerous
Because if you are not using early notification system like DNS blacklist monitor software you may not know the issue unless some users begin to complain and in this case you will lose a lot of email outbound messages which are not recoverable and users have to send these emails again. for example if your email server public IP address accidentally blacklisted at 9 AM and you know about the problem at 11 AM then begin to troubleshoot and resolve the issue at 11:30 AM.
so you loose outbound messages between 9 AM and 11:30 AM and you have to told users about this issue to resend their emails if it didn't reach recipients.
you will also note that some recipients may send you a rejected message and others may not.