E-Mail IP Whitelisting

In email systems, IP whitelisting is a technique used to allow incoming messages only from specific IP addresses that have been deemed trustworthy. By using a whitelist, email systems can help ensure that trusted sources are able to send messages, and can improve the security and reliability of the system.

What is an IP whitelist?

An IP whitelist is a list of IP addresses or even whole networks that have been identified as trusted sources. These IP addresses are typically allowed to bypass filters like IP blacklists or other security measures that are in place.

How does an IP whitelist work?

When a server receives an incoming connection from an IP address, it checks the address against its list of known whitelisted IPs. If the address is on the list, the connection is immediately accepted and the server will allow the communication to proceed without or with reduced restrictions like bypassing any used IP blacklists. This allows trusted users and systems to access the network or system without having to go through additional security checks which may stop communication.

How do IP addresses end up on a whitelist?

There are many ways that an IP address can end up on a whitelist. In some cases, an administrator may manually add the address to the list if they trust the source and want to grant it prioritized access. In other cases, an IP address may be automatically added to the list based on certain criteria, such as reputation or being an important communication partner.

What are the benefits of being on an IP whitelist?

As most IP whitelists are placed before IP blacklists, a by mistake added blacklist is not applied due to configuration. If you manage your own IP whitelist you can add important senders, services, IPs or even IP ranges to this whitelists.

You can use whitelists to rise reputation in spam filtering systems like rspamd or Spamassassin.

You can use externally controlled IP blacklists, which may list for you important mail services. These are skipped, as an IP whitelist has a higher priority.

Can an IP address be removed from a whitelist?

In some cases, an IP address can be removed from a whitelist. This typically requires the administrator who added the address to the list to manually remove it, or to update the criteria that were used to automatically add the address to the list.

As adding an IP address to a whitelist in email systems is mostly a point of reputation. Being removed from a whitelist is a big loss in reputation, which should be avoided.


IP or even network whitelisting is an essential part of email service management.

Overall, IP whitelisting can be an effective way to improve the security and reliability of an email system, but it requires careful management to ensure that it is effective.