If your server is caught sending out unsolicited emails, on a volunteer basis or not, your server - or at least, its IP address, will eventually be blacklisted. The most known and used blacklists are:
- SBL (Spamhaus block list)
- UCEProtect RBL
- CBL (Composite Blocking List)
- PSBL (Passive Spam Block List)
- Hotmail/Outlook (Subscribing to Microsoft JMRP and SNDS)
Note: The lists do not limit themselves as spam. Some may also keep notes of servers caught for hacking attempts.
Essentially, these blacklists keep a record of IP addresses caught sending out unsolicited emails and inserts them in a database.
Internet service providers, Mail Server owners, ... may then, at their sole discretion, choose to use these blacklists to help determine whether an email is coming from a known spam source or not, and react accordingly (mark the emails as spam, reject the incoming emails, block the blacklisted IP, ...).
It can happen that your server is exploited to send out emails and that you are eventually listed in a blacklist, you will have to rectify the situation and then contact the organization that has listed your IP address to request the removal from the blacklist ("delist").
Here are two resources that query a lot of well known blacklists, in which you may verify if your IP address is blacklisted:
- MXToolbox: Type in your IP address in the "Server IP" box and click on blacklist check.
- DNSStuff: (May request you to sign up in order to use their service)
In the IP Tools section, you will have "Spam database lookup" box - Type in your IP address and click 'lookup'.
If our Security & Abuse department sent you one or many notifications claiming abuse of our Acceptable Use Policy and you do not know how to fix the problem, you may create a Support Ticket via your Customer Hub. Our system administration team will then be able to analyze the integrity of your server.
Delisting IP addresses from Realtime Blackhole Lists (RBLs)