A. If you are using hosting:
- one of the customer sharing your IP are sending spams
- one of your staffs account got compromised and is used to send spams
B. If you are having your own server:
- one of your staffs account are compromised and is used to send spams
- one of your machines in your company is infected and is sending spams
- your mail server is compromised
IP blacklisting occurs because some emails are actually “traps” or what the industry calls “honey pot” that is set by security companies to be used to lure spammers. These email addresses are typically hidden from plain sight but could be scrap from websites by hackers and spammers.
When a particular machine or account is used to send spams, it often will send to one of these addresses that it collected and that results in getting your IP blacklisted.
The other reason how IP Blacklisting occurs is when a lot of entities lodge a complain against your IP for sending spam content.
When IP Blacklisting occurs, you will not be able to send any emails to your clients or customers that uses Email filtering or firewall with antispam.
The best solution to totally avoid getting blacklisted is to use a cloud Anti-spam that could detect OUTGOING mails. InternetNow recommends using AntispamEurope Email security service to prevent you from ever getting blacklisted.