Understanding IP Whitelists and IP warmups


Understanding IP Whitelists and IP warmups

IP Whitelist:

Have you ever used the word “blacklist” in your regular life? Of course yes, we use this term to define people that we are not getting along with; people that we want to block in our real life.

But aren’t there any whitelisted people? People that you welcome in your life. Sure there are, and hopefully a lot.

This same example is also applicable for IPs. An IP Whitelist is the process of creating a list of IP addresses or domain names that are welcome to send you emails without being interrupted by any spam filters. These are the list of trusted users.

Like if you have security guards at a gate of a certain event and you provided these guards with a list of names that are allowed to enter the event. This list is the IP whitelist and the guards are the spam filters that check the list of trusted users and allow them to pass the filtering process and be received to the inbox.


Besides having a list of trusted IPs you could also have a list of trusted programs to be executed safely or if not listed to not be executed and to be blocked.

The good advantage of using IP whitelist is that it allows only the emails of the listed IPs to be received, but the disadvantage is that it block anything that is not listed, that could be an important not harmful email with an unlisted domain or IP, as for salesperson for example, it’s not so useful to use whitelisting as they are exposed to receiving new emails from new IPs daily as their communications grow.

IP Warmup

If you ever watched a football match you will notice that all players are warming up before the match in order to be ready to play well with less risk to be injured.

The same for your email IP, it has to warmup in order to prevent injuries.

Let me rephrase this in term of “IP Warmup definition”, a user should gradually increase the number of emails sent using his dedicated IP which helps increase the user credibility and reputation with the Internet Server Providers(ISP) which leads to increase deliverability of the user’s email and keep his message away from being spammed.

When ISP notice an email sent from an IP that has not been used since a long time ago or a new IP, it starts monitoring and filtering that IP and may flag it. ISP also monitors your recipients’ reaction and response to your emails so they could identify if you are a legal sender or a spammer.

To build this reputation you have to start this sending emails flow gradually and do not send lots of emails all of a sudden as this will also be detected by ISP and may risk marking your IP as a spammer. So warming up gradually gives your ISP the chance to identify your sending flow and recognize your sending pattern.

Important things to know before warming up:

You need to know your ISP limitations, each ISP has a daily limit on the number of sent emails. If you exceed this limitation you will be blocked from sending emails. So you need to take this limit into consideration while scheduling your warmup.

Warmup is always used for dedicated IPs only, so if you have a shared IP you don’t need to warmup your IP as it’s already warmed up.

If your sending flow is less than 50K to 100K per month, you don’t need to warmup your IP as with this low volume of messages the ISP will not notice your existence so you can send your messages without bothering.

During warmup try to choose carefully your message content. Send messages that need a reply back or a welcome email or an email with transactional details that needs confirmation.

The below picture illustrates an example of IP warmup schedule: