Email being block by 88.blackzap.net – Frontbridge

Description:

Users are having problem sending email to some domain. From the error message you could see “smtp; 550 Service unavailable; Client host [xxx.xxx.xxx.xxx] blocked using 88.blacklist.zap; Mail From IP Banned To request removal from this list please forward this message to delist@frontbridge.com>”. You’ve check with known blacklist provider and none of them have your public IP listed.

Resolution:

The only way to get your public IP remove from their blacklist is through email. The list is proprietary and not open for public. You need to send them email asking for delisting and they will reply back to you in one business day. This is the case if you get listed the first time. But if you IP get listed again, the process would be more difficult and take much longer time.

Frontbridge is owned by Microsoft and its part of their Exchange Hosted Services. However the support seems only available on US working hour’s time. Other than that, there’re some false positive that could make good legitimate email being blocked.