How should I warm up an IP address or subdomain for email sending?
Matthew Whittaker
Co-founder & CTO, Suped
Published 15 Apr 2025
Updated 18 Aug 2025
8 min read
When you're launching a new email program, migrating to a different email service provider (ESP), or simply adding a new sending IP address or subdomain, one of the most critical steps to ensure your emails reach the inbox is warming them up. It's a foundational process that establishes trust with mailbox providers and builds a positive sender reputation from the ground up.
Think of it like training for a marathon. You wouldn't just jump into a 26.2-mile race without slowly building your endurance. Similarly, email providers need to see a gradual, consistent increase in your sending volume to determine that you're a legitimate sender, not a spammer. If you send a large volume of email from a brand new, cold IP or subdomain, it raises red flags and can lead to your emails being marked as spam, getting blocklisted (or blacklisted), or even being outright rejected.
The goal of warming up is to demonstrate consistent, good sending practices. This helps email providers understand your sending patterns and, over time, assign a positive reputation to your new IP and subdomain. A solid reputation is the cornerstone of excellent email deliverability.
Understanding email warming
Warming up an IP address or subdomain is a deliberate process of gradually increasing your email sending volume over a period. It's not just about the IP, as the domain reputation also plays a significant role. Even if your ESP provides a shared, pre-warmed IP, your specific subdomain still needs to build its own reputation with mailbox providers like Gmail and Yahoo. This is especially true when switching to a new subdomain for an existing, established mail stream.
The core principle is to start small and incrementally increase the volume. Mailbox providers assess your sending reputation based on various factors, including volume, frequency, bounce rates, complaint rates, and engagement. A sudden surge in volume from a new or previously unused IP/subdomain can be perceived as suspicious, leading to filtering or outright rejection. This is why IP warm-up is essential.
It's important to differentiate between warming up for a new mail stream (e.g., new sign-ups to a newsletter) versus moving an existing, high-volume list to a new sending infrastructure. For organic list growth, you typically don't need to force a warm-up, as the volume increases naturally. However, if you are migrating an established list, a structured warm-up plan is definitely the prudent approach. This is also true if you need to warm up new IP addresses for email sending, even if you keep the same domain.
Why warming up is critical
Without proper warming, your emails risk being sent straight to the spam folder, or even rejected, regardless of their content quality. This negatively impacts your deliverability and the effectiveness of your email campaigns.
Reputation building: Establishes a trustworthy history with mailbox providers. A new IP has no reputation, so you need to build it slowly.
Avoid blocklists: Prevents your IP from being flagged as suspicious and added to a blocklist (or blacklist), which can take time and effort to resolve. You can also monitor this with blocklist monitoring.
Consistent deliverability: Ensures your emails consistently land in the inbox, leading to better engagement and ROI.
Developing your warm-up schedule
The specifics of a warm-up schedule can vary based on your sending volume and the age of your IP or subdomain, but the general principle remains the same. You need to start with a very low volume and gradually increase it. It's often recommended to begin with your most engaged subscribers, as this helps generate positive engagement signals.
A common strategy involves increasing your sending volume by a small percentage each day or week, usually between 10-20%, but sometimes more aggressively depending on the mailbox provider and your list quality. Consistency is key. If you pause sending for a significant period, your IP might cool down, requiring a partial re-warm-up. The duration for warming up an IP address can vary significantly, from a few weeks to several months for very high volumes.
When you're warming a new IP address or subdomain, ensuring your DNS records are correctly configured is paramount. This includes SPF, DKIM, and DMARC records. These authentication protocols help prove that your emails are legitimate and prevent spoofing, which is a key factor in building trust with mailbox providers. Misconfigurations can lead to significant deliverability issues even before you start sending volume.
Week
Daily volume
Week 1
500-1,000 emails
Week 2
1,000-2,500 emails
Week 3
2,500-5,000 emails
Week 4
5,000-10,000 emails
Week 5+
Gradual increases based on performance and engagement
Example SPF record for your subdomaindns
v=spf1 include:spf.example.com ~all
Prioritizing content and engagement
The type of emails you send during warming is crucial. Transactional emails, like order confirmations, password resets, or shipping notifications, typically have high open and click rates because recipients are expecting them. These high engagement signals are invaluable for building a positive reputation quickly. Marketing emails, especially promotional ones, can be less engaging and might carry higher risk of complaints or unsubscribes, making them less ideal for initial warm-up phases.
Beyond the content, the quality of your recipient list is paramount. Always send to opted-in, engaged subscribers during your warm-up. Sending to old, unengaged, or purchased lists can introduce spam traps, increase bounce rates, and lead to complaints, all of which severely damage your nascent reputation and can get your IP or domain placed on a blocklist. For businesses sending B2B emails, there are also specific strategies to warm up your IP address for B2B sends.
Maintaining a consistent sending schedule during warm-up is also important. Mailbox providers learn your patterns over time. Erratic sending, or long periods of inactivity followed by bursts of high volume, can look suspicious. If you typically send once a week, tailor your warm-up plan to that frequency, even if it means taking longer to reach your full desired volume. The goal is to match your future sending habits as closely as possible.
Transactional emails
Emails recipients expect, such as:
Order confirmations: Immediately expected after a purchase.
Password resets: Requested by the user for account access.
Shipping updates: Timely information about deliveries.
Account alerts: Notifications about account activity.
Marketing emails
Promotional or informational emails, such as:
Newsletters: Regular updates about products or services.
Promotional campaigns: Sales, discounts, or new product announcements.
Re-engagement campaigns: Efforts to reactivate dormant subscribers.
Monitoring and adapting your strategy
During the warm-up period, vigilant monitoring of your email deliverability metrics is non-negotiable. Pay close attention to your open rates, click-through rates, bounce rates, and complaint rates. Tools like Google Postmaster Tools and other analytics platforms provide invaluable insights into how mailbox providers are perceiving your emails.
If you notice a sudden drop in deliverability, an increase in bounces, or a rise in complaint rates, it's a clear signal to pause your volume increase or even reduce it temporarily. Investigate the cause immediately. It could be due to list quality issues, content flagging spam filters, or unexpected blocklisting. Addressing these issues promptly is crucial for maintaining your progress.
Remember, the goal is to build a long-term, positive sending reputation. This process isn't just a one-time task; it requires ongoing attention to your email program's health. Continually clean your lists, monitor engagement, and adapt your sending practices based on performance data. By doing so, you ensure your IP address and subdomain remain trusted senders, leading to optimal inbox placement.
A crucial aspect of monitoring includes checking for email blocklist (or blacklist) status. Even during a carefully executed warm-up, issues can arise. Regularly checking if your IP or subdomain has appeared on any major blocklists can help you react quickly and mitigate potential damage to your sender reputation. Being proactive in this area saves significant time and effort in the long run.
Common pitfalls to avoid
Sending too much too soon: This is the quickest way to get flagged as spam. Always adhere to a gradual increase.
Poor list quality: Sending to unengaged or old contacts, or purchased lists, will lead to high bounces and complaints.
Inconsistent sending: Large gaps or erratic spikes in volume can negatively impact your reputation.
Ignoring metrics: Failing to monitor bounce, complaint, and engagement rates means you'll miss warning signs.
Views from the trenches
Best practices
Start with your most engaged subscribers and high-value transactional emails.
Maintain a consistent sending volume and frequency during the warm-up period.
Monitor your deliverability metrics closely, including open rates and bounce rates, to quickly identify and resolve any issues.
Ensure all DNS records, including SPF, DKIM, and DMARC, are correctly configured.
Be patient, as building a strong sending reputation takes time and consistent effort.
Common pitfalls
Attempting to send too many emails too quickly from a new IP or subdomain, leading to blocklisting.
Sending to unengaged or low-quality lists, which increases bounce rates and spam complaints.
Neglecting to monitor deliverability metrics, missing early warning signs of reputation issues.
Stopping or drastically reducing sending volume during the warm-up period, causing IP cooldown.
Not having proper authentication (SPF, DKIM, DMARC) in place before starting to send.
Expert tips
For weekly sends, adjust your warm-up schedule to match that frequency, understanding it will take longer.
Warming up is most critical when migrating an existing, high-volume mail stream to new infrastructure.
Ensure your existing mail stream is healthy with high engagement and low complaints for 1-2 months before any changes.
If changing IP, DKIM, and domain combinations, a structured warm-up is the prudent approach.
For new organic list growth, you can let the reputation build naturally rather than forcing a warm-up.
Expert view
Expert from Email Geeks says that the purpose of a warm-up plan is to familiarize mailbox providers with both the volume and frequency of email to expect from a new IP. A dedicated IP might not be necessary if it only sends once a week, but warming is still required for that frequency.
2020-01-03 - Email Geeks
Expert view
Expert from Email Geeks says that warm-up plans are primarily for when an existing mail stream is being moved to a new IP address. It is not necessary to warm up in anticipation of natural organic list growth, as providers will not penalize for that.
2020-01-03 - Email Geeks
Your path to optimal deliverability
Warming up an IP address or subdomain is a non-negotiable step for any sender aiming for high email deliverability. It's a strategic process that builds trust with mailbox providers, reduces the risk of being blocklisted (or blacklisted), and ensures your messages reach your audience's inboxes. By adhering to a gradual increase in sending volume, prioritizing engaged recipients, and consistently monitoring your metrics, you lay the groundwork for a robust and reliable email program.
The patience and attention to detail during this initial phase will pay dividends in the long run, safeguarding your sender reputation and maximizing the effectiveness of your email communications. Embrace the warm-up process as an investment in your email program's success.
Gmail and 
Yahoo. This is especially true when switching to a new subdomain for an existing, established mail stream.
Google Postmaster Tools and other analytics platforms provide invaluable insights into how mailbox providers are perceiving your emails.
