What are best practices for warming up new IPs for transactional emails?
Michael Ko
Co-founder & CEO, Suped
Published 6 May 2025
Updated 17 Aug 2025
8 min read
Transactional emails are the backbone of many businesses, ensuring critical communications like password resets, order confirmations, and account verifications reach your users. When you're setting up new IPs for these essential messages, a proper warm-up strategy isn't just a best practice, it's a necessity. Skipping this crucial step can quickly land your IPs on blocklists (or blacklists), severely impacting your deliverability and customer experience.
The goal of IP warming is to establish a positive sender reputation with Internet Service Providers (ISPs) and email clients. They monitor your sending behavior, and a new IP address starts with a neutral reputation. Sending too much volume too quickly signals suspicious activity, leading to blocks and missed inboxes. For transactional mail, where recipients expect your messages, consistently positive engagement is your greatest asset in building this reputation.
Understanding IP warming for transactional volume
Warming up new IP addresses for transactional emails is about building trust with ISPs like Google and Microsoft. A new IP address starts with a neutral reputation, and sudden high volumes of email from an unestablished IP are a major red flag, often signaling spam. Instead, you need to gradually increase your sending volume, allowing ISPs to see consistent, positive engagement from your recipients. This methodical approach helps them recognize your legitimate sending patterns and assign a positive reputation to your IP address.
Transactional email typically has high engagement rates, which is an advantage during the warm-up process. Recipients usually expect and interact with these messages, sending positive signals to ISPs. This consistent, desired interaction is what helps your IP build a strong sender reputation over time, ensuring your important emails land in the inbox rather than the spam folder.
Even if you anticipate very high volume, starting slowly is non-negotiable. Trying to accelerate the process too quickly can trigger spam filters and lead to your IPs being blocked. Remember, the goal is to demonstrate consistent and welcome sending behavior. We have an article that goes into the best IP warm-up strategies for email sending.
Setting up your technical foundations
Before you send your first email from a new IP, ensure all your technical ducks are in a row. Proper authentication is paramount for establishing sender legitimacy. This includes setting up SPF, DKIM, and DMARC records correctly for your sending domains. These protocols verify that your emails are indeed coming from your authorized servers, preventing spoofing and enhancing your sender reputation. For a comprehensive overview, read our simple guide to DMARC, SPF, and DKIM.
Beyond authentication, maintain clean and engaged recipient lists. For transactional emails, this usually means sending only to active, opted-in users who genuinely expect your communications. Avoid sending to old, unengaged, or unverified email addresses, as this can lead to bounces, spam complaints, and eventually, blocklistings. Regularly validate your email lists to remove invalid or risky addresses before sending.
Authentication Protocol
Purpose
SPF (Sender Policy Framework)
Authorizes specific IP addresses to send emails on behalf of your domain.
DKIM (DomainKeys Identified Mail)
Digitally signs your emails, verifying content integrity and sender identity.
Builds upon SPF and DKIM, providing reporting on email authentication failures and instructing receiving servers how to handle messages that fail authentication.
DNS records
Ensure all relevant DNS records are correctly configured and propagated.
Implementing these measures is a fundamental step in ensuring your emails are trusted by ISPs. Without them, even low-volume transactional sends can struggle to reach the inbox. We have another article that covers best practices for email IP warm-up when switching ESPs.
Strategic volume scaling for new IPs
The core of IP warming involves gradually increasing your email volume. This isn't a race, it's a marathon. For transactional emails, starting with your most engaged users is a highly effective strategy. These are the recipients who are most likely to open and click your emails, providing the positive engagement signals that ISPs look for. Begin with a very low daily volume and slowly ramp up over several weeks, or even a couple of months, depending on the total volume you aim to reach. A typical warm-up schedule for a dedicated IP can range from 15 to 60 days, as suggested by this Rejoiner guide.
It's also crucial to maintain a consistent sending cadence. Irregular sending patterns, or sudden spikes after periods of inactivity, can negatively impact your sender reputation. ISPs prefer predictable sending behavior. If you anticipate large seasonal fluctuations, try to gradually adjust your volume rather than making abrupt changes. For more insights on this, Twilio SendGrid offers a comprehensive guide on IP warm-up.
The problem with warming too many IPs
When dealing with very high volumes, such as 10 million emails per month, it's rarely necessary to warm up dozens of IPs simultaneously. Attempting to do so can make your sending appear suspicious to ISPs. This behavior, sometimes called "snowshoeing," is a common tactic used by spammers where mail is distributed across many IPs to avoid detection. Instead, focus on building a strong reputation on a few, highly utilized IPs.
Understanding IP warming strategy and email volume scaling is crucial. Over-provisioning IPs can lead to unnecessary complications and potential deliverability issues. The focus should always be on quality over quantity, building a solid sender reputation with a manageable number of IPs that align with your actual sending needs.
Common pitfalls and how to avoid them
Common pitfalls
Rushing the IP warming process by sending too much volume too quickly. This is a common trigger for spam filters and can lead to immediate blocklistings.
Using unsegmented, old, or uncleaned email lists for warming. This dramatically increases bounce rates and the risk of hitting spam traps, which are detrimental to your sender reputation.
Neglecting to monitor your IPs for blocklist (or blacklist) placements during the warm-up period. Delayed detection means longer recovery times and continued deliverability issues.
How to avoid them
Adhere strictly to a slow and steady volume increase, ideally over several weeks. Patience is a virtue in IP warming, even for transactional emails.
Regularly clean and validate your email lists to ensure you're only sending to active, legitimate recipients. This minimizes bounces and spam complaints, preserving your reputation.
Implement continuous blocklist monitoring to catch any listings immediately and address them. Early detection is key for minimizing damage.
If you find your IPs unexpectedly on a blocklist, it often points to an underlying issue with your sending practices or recipient engagement. Early detection through constant monitoring allows for quick remediation, minimizing long-term damage to your sender reputation and deliverability. You can learn more about blocklists in this guide to email blocklists. Also, understanding why your emails are going to spam can help prevent future issues.
High bounce rates and spam complaints are detrimental to your sender reputation and can derail your warm-up efforts. Regularly cleaning your list is essential, not just for warming but for ongoing deliverability success. Consider monitoring your sender reputation through Google Postmaster Tools, which can provide insights into your email performance and spam rates.
Optimizing for engagement and reputation
For transactional emails, engagement is naturally high, but you can still optimize to ensure maximum positive signals. Make your transactional emails clear, concise, and immediately recognizable. Ensure your subject lines are descriptive and your calls to action are obvious. Positive engagement, such as opens and clicks, tells ISPs that your emails are wanted and valued by recipients. This positive feedback loop is critical for maintaining a healthy sender reputation.
Beyond initial warming, continuous monitoring of your email performance is vital. Pay close attention to deliverability metrics such as open rates, click-through rates, bounce rates, and spam complaint rates. Tools that provide insights into your inbox placement can help you identify and address issues before they escalate. A low spam complaint rate, ideally well below 0.3%, is crucial for good standing with major ISPs. Regular review of these metrics allows you to fine-tune your sending strategy and ensure long-term email deliverability.
Ultimately, the best practices for warming new IPs for transactional emails revolve around proving you are a legitimate, high-quality sender. This means sending wanted mail to engaged recipients from a properly configured infrastructure, and scaling your volume responsibly. When you do this, ISPs will reward you with better inbox placement, ensuring your critical transactional messages always reach their destination.
Views from the trenches
Best practices
Start with low sending volumes, typically in the 2-10 email range per day per IP, gradually increasing over time.
Assign dedicated IPs to individual large customers and allow them to warm their IPs independently.
Maintain a low spam complaint rate, aiming for well below 0.3% to meet major ISP requirements.
Focus on quality over quantity: use fewer IPs effectively rather than over-provisioning many IPs for a single sender.
Common pitfalls
Attempting to warm up too many IPs at once, which can make your sending appear suspicious to ISPs.
Rapidly increasing sending volume from zero to millions of emails per month, triggering spam filters.
Ignoring blocklist notifications and not proactively monitoring your IP reputation during the warm-up process.
Setting a high internal spam rate tolerance (e.g., 0.5%) for transactional emails, which is too lenient for modern standards.
Expert tips
Be patient when dealing with blocklist removals, as some services may have daily submission limits.
Consider hiring a deliverability consultant for significant increases in email volume to navigate potential challenges.
Ensure rigorous spam detection and prevention systems are in place, even for trusted customers, to avoid abuse.
Do not rely solely on FBLs for monitoring complaints, as many ISPs do not provide them.
Expert view
Expert from Email Geeks says waiting for Spamhaus removals to process is the best course of action when faced with a blocklisting.
2024-05-11 - Email Geeks
Expert view
Expert from Email Geeks observes that warming up 60 IPs at once for a small number of customers can make you appear as a 'snowshoer', a technique spammers use.
2024-05-11 - Email Geeks
Final thoughts on IP warming
Warming up new IPs for transactional emails is a critical process that lays the foundation for excellent email deliverability. It demands patience, meticulous attention to technical setup, and a strategic approach to volume scaling.
By adhering to best practices, prioritizing recipient engagement, and consistently monitoring your performance, you can build a robust sender reputation that ensures your vital transactional messages reliably reach their intended inboxes. This proactive approach not only helps you avoid common pitfalls like blocklistings but also optimizes your email ecosystem for long-term success.
Google and 
Microsoft. A new IP address starts with a neutral reputation, and sudden high volumes of email from an unestablished IP are a major red flag, often signaling spam. Instead, you need to gradually increase your sending volume, allowing ISPs to see consistent, positive engagement from your recipients. This methodical approach helps them recognize your legitimate sending patterns and assign a positive reputation to your IP address.
