The Essential Guide to IP Warming: Building Your Email Reputation Step-by-Step

What is IP Warming?

IP warming involves methodically sending emails in gradually increasing volumes to establish a reputation as a legitimate email sender. When you start sending from a new ,or “cold”, IP address, Internet Service Providers (ISPs) have no data to determine whether you are a spammer or a legitimate sender. By starting small and slowly increasing the volume, you provide them with a positive sending history, demonstrating that you are not a threat.

Without a proper IP warming process, your emails might end up in spam folders, drastically reducing the effectiveness of your campaigns.

As we delve further into the specifics of creating an effective IP warming schedule and discuss the best practices to ensure optimal results, it's important to have a clear understanding of the terminology used.

Glossary of Terms

IP (Internet Protocol) Address

ISP (Internet Service Provider)

IP Warming

Sender Reputation

Email Deliverability

SPF (Sender Policy Framework)

DKIM (DomainKeys Identified Mail)

DMARC (Domain-based Message Authentication, Reporting, and Conformance)

Email List Hygiene

Pre-Warming Checklist for Email Deliverability

Before beginning an IP warming process, it's essential to have certain elements in place to ensure the effectiveness of your campaign and to safeguard your sender reputation. Here’s a comprehensive pre-warming checklist that covers all necessary preparations:

Verify Email List Health

Remove invalid, inactive, and bounced email addresses.
Segment out subscribers who haven’t engaged in a long time and try a re-engagement campaign or remove them if unresponsive.

Ensure Proper Authentication

Verify that your SPF record is correctly published in DNS. This helps ISPs verify that you are authorized to send emails from your domain.
Ensure DKIM is set up to add a digital signature to your outgoing emails, further establishing their legitimacy.
Set up a DMARC policy to instruct ISPs on how to handle emails that don’t pass SPF or DKIM checks.

Review and Optimize Email Content

Check your email content for words or phrases commonly associated with spam and adjust accordingly.
Ensure that emails are responsive and look good on mobile devices.
Make sure every email includes an easy-to-find unsubscribe link.

Test Email Deliverability

Before starting the full warming process, send test emails to a variety of email providers to see how your emails are being received.
Utilize deliverability testing tools to preview inbox placement and spam scores.

Set Up Monitoring and Analytics

Implement tools to monitor deliverability and reputation in real-time.
Define key performance indicators (KPIs) such as open rates, click-through rates, bounce rates, and spam complaints to track throughout the warming process.

Legal Compliance

Ensure all your email marketing practices comply with laws such as CAN-SPAM, GDPR, or other relevant regulations, depending on your audience's location.

Having these elements in place before beginning IP warming not only facilitates a smoother and more successful warming process but also helps in building and maintaining a robust sender reputation.

Understanding Sender Subdomains

When managing a large or diverse set of email types (e.g., transactional emails, marketing blasts, newsletters), it's common practice to use sender subdomains.

A sender subdomain is a subset of your main domain that helps segment and manage different types of email communications more effectively. Examples might include news.yourdomain.com for newsletters or offers.yourdomain.com for promotional emails.

Why Use Sender Subdomains?

Using sender subdomains can help improve email deliverability and sender reputation in several ways:

Reputation Management: Subdomains allow you to isolate the reputational impact of your various email campaigns. For instance, if your promotional emails are marked as spam, this will not directly affect the reputation of your transactional email subdomain.
Targeted IP Warming: Each subdomain can be associated with a different IP address, allowing tailored IP warming strategies based on the specific email types and their unique sending behaviors and volumes.
Improved Email Tracking: Subdomains make it easier to track the performance and engagement of different email types, facilitating more detailed analytics and insights.

Do You Need to Warm All Sender Subdomains Individually?

Yes, if you are using multiple subdomains each associated with its own dedicated IP address, you need to warm up each IP address individually. Here’s why:

ISP Recognition: Internet Service Providers (ISPs) track and evaluate sender reputation at both the domain and IP address levels. When you introduce a new IP address, even if it's under the same main domain, it is essentially starting from scratch in terms of reputation.
Volume and Type of Email: Different types of emails often have different volumes and engagement patterns. For example, transactional emails typically have higher open rates than promotional emails. Warming up IPs based on the specific characteristics of the emails they send ensures optimal deliverability.
Risk Mitigation: By warming each IP individually, you mitigate the risk of damaging your overall domain reputation. If one type of email content begins to receive a high level of spam complaints, the separate IPs ensure that this negative feedback affects only the specific subdomain’s IP, not your entire email ecosystem.

How to Warm Up Each Sender Subdomain

The process of warming up a sender subdomain’s IP involves gradually increasing the volume of emails sent from that IP over a period of time. Here are some steps to follow after completing your pre-warming checklist:

Build your Campaign: Design a relevant email campaign that makes sense for your entire audience that you can use throughout the IP warming process. Ensure your email has a strong subject line and call-to-action. For example, if you are warming a promotional IP address, a call to action with a large, exclusive discount may result in higher CTRs.
Start with Low Volume to a Highly Engaged Audience: Begin by sending a small number of emails (around 50) from the new IP address. You can first target employees of your company and ask them to open and click, or a highly-valued segment of your subscriber base that is most likely to engage.
Monitor Engagement: Pay close attention to how these initial emails perform. Look at open rates, click-through rates, and, importantly, spam complaints.
Gradually Increase Volume: If the initial emails perform well, gradually increase the email volume by no more than 50% each day. Continue monitoring performance and adjust if needed.

By carefully managing the warming process for each sender subdomain, you ensure that each segment of your email strategy builds a strong, independent reputation with ISPs, leading to better overall email deliverability and campaign success.

Example IP Warming Schedule

While there is a more conservative and more aggressive approach to IP warming, we’ve never had any issues when following Braze’s IP warming schedule. Their recommendation is to follow this strict plan, without skipping a day:

DAY	# OF EMAILS TO BE SENT
1	50
2	100
3	500
4	1,000
5	5,000
6	10,000
7	20,000
8	40,000
9	70,000
10	100,000
11	150,000
12	250,000
13	400,000
14	600,000
15	1,000,000
16	2,000,000
17	4,000,000
18+	Double Daily Until Desired Volume

Conclusion: Maintaining Momentum in IP Warming

Successfully warming up your IP is an important step towards establishing a reliable and efficient email marketing system. However, it's crucial to understand that the work doesn't end once the initial IP warming process is completed.

Most Internet Service Providers track sending reputation over a rolling period, typically storing data for only about 30 days. This means that consistency in your email sending is just as important as the initial efforts you put into warming your IP.

If you stop sending emails for a month or longer after the warming process, you risk erasing all the hard-earned reputation you've built up. ISPs might treat your subsequent emails as if they are coming from a new or "cold" IP again. This would necessitate a repeat of the IP warming process to rebuild trust, costing you time and potentially impacting your reach and engagement rates negatively.

Therefore, it's essential to maintain a regular sending schedule even after your IP is fully warmed up. This does not mean you need to send large volumes constantly; rather, it's about keeping a consistent (and relevant) presence in your subscribers' inboxes.