Secret of IP warming – Plans, Schedule, Strategy & Pitfalls

IP warming or IP warm-up is strategically sending a low volume of emails and increasing it slowly. Basically, this is done to build IP reputation and domain reputation. So that ISP (Internet Service Providers) not only accepts large email volume from your server but also delivers them straight to the inbox. In this tutorial, you will learn to plan, schedule, and create the perfect strategy for IP warming. You will also learn some of the pitfalls of IP warming.

What is IP warming?

When you buy new IP or create a self-hosted SMTP server then the reputation of the IP is neutral in most cases. Therefore, somehow you have to increase its reputation. Now, you might want to ask the next question.

What is IP reputation and why does it matter?

IP reputation is the credibility of IP in the eye of ISP as good or bad depending on its past history. If it’s a good one then ISP lets the owner send bulk emails from the IP. But if it’s neutral of a bad one then still ISP will let the owner send emails but not the bulk one. Also, not all emails might get to see inbox.

IP reputationDelivers toBulk Emailing
GoodInbox mostlyPossible
NeutralInbox or SpamVery Limited Possibility
BadSpamNot Possible

I hope the above table makes it very clear where your email is going to depend on IP reputation. But wait you must not think it’s the sole deciding factor. It is just one of the factors on which inbox delivery depends.

How to improve IP reputation?

The answer is IP warm-up. As I already discussed IP warm-up is a gradual process of increasing email volume. Now, when you create a new SMTP server or add new IP to an existing server, you should start with sending a small number of emails to multiple ISP.

When you send an email out for the first time you will see some ISP deliver your email to spam. Nothing disheartening, this is absolutely fine. Since your server is new, they are simply not trusting you. They first evaluate the traffic from the new IP or “cold” IP address and since they haven’t seen any traffic coming from your IP in past, they might choose to put your email to spam. And that’s why we are warming IP, to gain the trust, to deliver into inbox.

Obviously, you would have sent first few emails to yourself. Now, if emails went to spam, move those emails to inbox and write a reply.

Next, we are going to devise a plan. So lets start.

The Perfect Plan for IP Warming

Now, you understand IP warming, let’s ensure that some stuffs are in place actually.

Pre Warming Checklist

  • Check for IP blacklist.
  • Check for all email security protocols like DKIM, DMARC, SPF, PTR (reverse DNS), MX, etc.
  • Create accounts for feedback loop complaints with all available ISP
  • Microsoft blocks all IP addresses in the subnet (256 IPs) if any single IP in that subnet found to be involved in spamming. Therefore, it’s very important to register with Microsoft Smart Network Data Services (SNDS). Also, monitor it for junk reporting.
  • Never forget to include the List-Unsubscribe header for your promotional emails.
  • If possible get Return-Path certification.

After, checklist it’s time to devise perfect plan to IP warming.

  1. First, collect the email addresses of your friends, family (you may call it a seed list). Those email addresses must include multiple ESPs. Getting only Gmail, Outlook, or Yahoo mail is not sufficient.
  2. Then, send emails to yourself or your friends, family for a week or at least 2-3 days. If your emails go to junk, move to inbox and also ask recipients to move it to inbox.
  3. Next, get as many replies as possible. Two-way communication is key to a quick IP warmup.
  4. Do not rush and wait until you start getting all emails delivered to inboxes.
  5. Then send emails to your double opt-in customer, where chances of customer interaction with your emails are super high.
  6. If you don’t have a double opt-in customer, then for cold email send highly lucrative emails to customers.
  7. Do not send UCE (Unsolicited Commercial Emails) or spam during warmup. This will deteriorate your IP reputation instead of building one.
  8. Continue to send emails out from your server on regular basis, otherwise, its reputation will be lost

The Perfect Schedule in Imperfect World

Now you understand the steps involved in warming up, it’s time to create schedule.

The IP warm up schedule

DayGmailYahooOutlookAOLMailComcastAny other ISP where you
want to deliver emails. x 4

For the following schedule make sure not to exceed 500 emails per hour per ISP. That you can raise further to 1000 emails per hour per ISP after you have reached a limit to 10,000 emails

IP Warmup Schedule

You can also make changes into schedule as per your requirement. This is not hard and fast rule. If emails goes to spam on any day don’t increase the volume next day.

The Great IP Warmup Strategy

Now we have plan and schedule ready. You might want to ask why do we need strategy. The answer is though plan and schedule is for perfect scenario but that’s going to happen in limited scenario.

Chances are that your emails goes to spam straight on very first day. Or, perhaps emails got rejected straight away from the ISP.

Emails went to spam on day 1

  • Go through the checklist once again. If all is well then check your score at mail-tester and read why emails go to spam.

Emails started to go into spam on day X

  • Do not increase the volume the next day in fact, fall back to day X-2 volume or pause for a day. Make sure all emails go to inox, then only increase.
  • Change your email template.
  • Check for spam reporting & unsubscription.
  • Make sure you got bounces working and do take a note of the bounce rate. More than 5% of the bounce rate is dangerous.
  • Clean your email list with any of the email validators.
  • Check for honey trap emails in your list. You can also download the 10 million spam trap list by signing up here.
  • If any ISP is imposing a policy block don’t send any more emails to them, unless blockage has been removed.

The Pitfalls

First of all, many of you believe once IP had been warmed up, you don’t have to warm up again. That’s a partial truth. The fact is that if you don’t send emails regularly your IP reputation is bound to go away.

Second, if a recipient reports spam then that hurts your IP reputation and for that you have to compensate. One way is to continued IP warm up or get good interaction from other recipients.

Third, IP warmup is only one aspect of IP reputation but there is a lot of other factors you need to take into consideration like domain warmup. Also, don’t use negative words, or at least minimize the use of them.

Fourth, IP warmed up for one ISP won’t work for another ISP. You have to work upon them independently.

Panacea of inbox delivery : Engagement

Now ISP’s algorithm is not limited to verifying email security protocols. They have evolved over the years and track subscribers’ engagement with an email and its sender as well as nature.

  • Actions that increase IP reputations are: Opening a mail, reading the mail, clicking on links & images, scrolling through the mail, spending time on that mail, adding the sender to the contact list.
  • Actions that decrease IP reputations are: Reporting the email as spam, moving it to the spam folder, unsubscribing the list, deleting the mail without reading or immediately after opening it.
  • Actions that don’t affect IP reputation: Ignoring mail completely.


At last, IP warming is not a rocket science. It’s just about patiently scaling up email volume. This applies to all ISP.

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