What is IP Blacklisting
Real Time Black List (RBL) are databases available online that ANTI-SPAM solutions CONSULTS. The FIX ip of your mail server will be block by these ANTI-SPAM solutions if RBL reports that the IP is in the database.
Any company that uses these solutions in ANTI-SPAM or firewall will not receive your email. Your IP is considered as BLACKLISTED. De-listing your IP will takes days or even weeks.
What Causes It?
Any compromised PC/notebook in office with malware could sent out thousands of emails. This is known as a spambot/zombie participant. An email account could have been hacked and used to send out spams.
Hide your fix IP by sending out using a secure set of IPs
Use an outgoing filter system that checks and count your emails to see if they are behaving like a bot/zombie/auto spams.
Notify you immediately of the situation and stop spams from going out further. You can identify the compromised pc/notebook/mailbox.
The public and hijackers will never see your public IP and minimizes any attempt to hack your email accounts.