What is SMTP Server Warm-up & How to do it.

If your emails go to SPAM there is no reason to worry.

Emails often land in a spam folder particularly for a new sender who has a new SMTP (Email) server, new IP, and Domain.

Even when precautions have been taken and all the technical aspects addressed such as DKIM, SPF, RDNS, DMARC, No Blacklists, and 10/10 Score on Mail-Tester.com, your emails could still land in spam.

After building a New SMTP Server that has a new IP Address, or subscribing to an SMTP Service such as Amazon SES with a dedicated IP, and before starting sending any of your email marketing campaigns, there is a need to warm up your IP Address.

You may also want to warm it up in case you had left your IP for 30 days or so without sending any email.

As such, SMTP warm-up should be a continuous process.

What is Warming Up IP?

Your new Brand IP Address for your SMTP does not have any reputation on the internet while ISPs (internet service providers) do not know the new IP. Hence, IP warmup refers to the practice of building your own reputation on the internet through a gradual increase of the volume of mails sent using your IP address as per a predetermined schedule.  

Upon noticing an email that suddenly came from a new IP address, ISP will immediately start evaluating the traffic that emanates from that IP.

Considering ISPs often treat email volume as important in determining spam, you can begin sending low email volume then gradually increase the number.

This would enable email providers an opportunity to observe and analyze your sending habits and volumes carefully then record how your recipients would treat your emails.  

How do ISPs evaluate your emails and Reputation?

ISPs evaluate your reputation when you begin the warming up process according to three main factors:

  1. Bounce Rate: when you embark on an email campaign, ensure your emails are valid because a high bounce rate destroys your reputation.
  2. Spam Traps: Note that even a small percentage of spam traps could end up blacklisting you!
  3. Spammy Content: The content of your messages is essential; ISPs monitor whether there are any spammy keywords or blacklisted links that you are using.
  4. User Interaction: The way recipients interact with your email is important because if they often report you as spam, it becomes a real problem.

Read More about Spam Factors and How you Land Your Emails in your inbox here.

Warming Up IP in Action (Examples)

We already have a big picture warming up SMTP, now we need to cite some examples and real scenarios in order to understand how the whole operation works.

Please Note: The sample schedules below are just suggestions. Different senders act differently

1000 Emails Per day: sending 1000 emails per day is not a big deal because, on the first day, you can start by sending 20 emails then you gradually increase the number to reach 1000 within 7-10 days. The following table describes how the schedule could be. 

10K Emails Per Day: Below is the scenario, it appears just like the schedule for 1000 emails but here the schedule is more extended.

For better results and to make things easier, always split large volume warmup campaigns into smaller ones. For instance, in our case, we can split it into at least three schedules. 

  1. Reach 10K emails.
  2. Reach 30K emails.

Some have said this makes the warm-up schedule longer which could be true to an extent but my experience is that you will manage and monitor your warming-up campaigns more easily and realize better results.

Hence, if you wanted to warm to 10K, the number of emails would be much less and it’s possible to see and also monitor the user interaction as well as the bounce rate for a smaller amount of emails. This makes the picture clearer.

Automatic Warm -Up


One of the most effective ways of ensuring that online reputation is high is through using of automated warm-up system which eliminates human error when doing it. It can be a costly affair but the best automated tool I have come across is what we use here at Rubedo

Email Volume and Timeline

When dealing with IP warm-up, the warmup schedule and the sending volume is always different for all senders.

The number of emails that you send will depend on your total email volume considering some may require you to send 100 emails daily while others might need 1M per day!

However, you must send enough emails at an adequate frequency to ensure your email reputation is possible to track.

Again, there is something important you should know; the majority of reputation systems will store data for only 30 days. Thus, do not go for 30 days or more without having to send on an IP. If that happens, you have to warm it up once more.  

I had earlier indicated that warming up an IP should be a continuous process.

Maintain Warm Up across ALL ISPS

One important aspect to always remember is that you should maintain that steady volume for the entire warmup period for every ISP.

For this reason, split up the warm-up schedule to ensure each ISP receives a comparable amount of mail every day. It means do not warm up Yahoo! on Tuesday, Gmail on Monday, etc. Always disperse your mail evenly to each ISP on each day of the warm up.

If not done that way, the sending activity would look sporadic and you may fail to build a very solid reputation.

The strategy is to mix things up! And not send to a single ISP at a time.

Warming up IP Tips:

The following are some important tips you can follow as you warm up IP:

  1. Do not start until you have got a High sending score: You can ensure this by configuring DKIM, SPF, rDNS, as well as other technical details I have explained in my courses in detail, and if interested, check here.
  2.  Do not think of sending promotional emails during the warmup period. If you need higher engagement rates, send transactional emails or more valuable info. 
  3. Only mail to the top active subscribers first and ensure the bounce rate is at 0%.
  4. Do not switch or rotate during warmup because rotation is another sign of spam.
  5. Add a clear link in your emails where people can unsubscribe. 
  6. It’s necessary to add an email signature to make your emails look more trusted. 
  7. You can mix your campaigns with premium SMTP services that give enhanced user interaction and more reputation of the domain.
  8. You can also join News Letters. They ensure a lot of your emails get to the inbox while giving you a higher domain reputation.
  9. Send to your friend’s list then ask them to report you as non-spam and also inform them to reply to the emails.
  10. Again, try building an audience and warm up to that particular audience. Through such a strategy, it’s possible to achieve the best user interaction, hence making the “warming up process” easier.
  11. Ensure to monitor your campaigns accurately while keeping your bounce rate below 2% by validating the email –I have been using Debounce Email validation service which is powerful and even cheap. 

How to Monitor IP Reputation?

Do you want to monitor your Bounce rate, reputation score, and user feedback?

Services such as Amazon SES and Spark post have over time built in a reputation system that would show the User Interaction and Bounce Rate.

As I had explained in my course, if you use a Custom SMTP: “Build Your Own SMTP and Send Unlimited Emails!” or any other SMTP you decide to use.

In some instances, you can monitor bounces and user feedback using a mailing system such as MailWizz.

You could also monitor, open, unsubscribe, and open rates. It indicates how users interact with your messages.

Monitor Reputation?

When you have the right tools for checking the IP reputation, then you are halfway to success. Some of the tools that you can utilize for such exercise include:

  • Senderscore.org by Return Path. The score here ranks from 0-100 with 100 being the best. It also tells you about your performance. It’s recommended that you should maintain your sender score at 90 or even better.
  • Senderbase.com by Cisco.  This tells you about your reputation across all network providers under Cisco management. Here the reputation score is grouped into Poor, Neutral, and Good.
  • Postmaster.live.com. Microsoft’s smart network data services provide you with information on traffic originating from your own IP address including the volume of sent emails, spam trap hits, and complaint rates.
  • Postmaster.google.com. This tool gives you access to data from your domain particularly on Google Search Console.
  • Postmaster.aol.com. Checks on your IP reputation and consequently rates it as “bad”, “neutral”, and “good”.