What are best practices for IP warming strategy and email volume scaling?
Matthew Whittaker
Co-founder & CTO, Suped
Published 27 Apr 2025
Updated 17 Aug 2025
8 min read
Starting with a new IP address for email sending or significantly increasing your email volume can feel like walking a tightrope. The primary goal is to establish a strong sender reputation with Internet Service Providers (ISPs), which is essential for consistent inbox placement. Without a proper IP warming strategy, your emails could end up in spam folders, or worse, be completely blocked.
IP warming is the methodical process of gradually increasing the volume of email sent from a new or cold IP address. This slow and steady approach allows ISPs like Google and Microsoft to observe your sending behavior. They look for signs of legitimate sending, such as low bounce rates, low spam complaints, and high engagement (opens and clicks).
Ignoring this crucial step can lead to your emails being flagged as suspicious, hurting your deliverability significantly. Think of it as building trust. You wouldn't suddenly send millions of emails from a brand new server and expect it to go smoothly. ISPs need to verify you're a responsible sender.
Developing a warming schedule
One of the first questions I get is, 'How quickly can I ramp up?' There's no universal magic number, as it depends on factors like the size and quality of your list, the engagement levels of your recipients, and the type of email content you're sending. However, a common principle is to start with your most engaged subscribers.
Begin by sending small volumes to contacts who consistently open and click your emails. This positive engagement signals to ISPs that your mail is desired, building a good reputation for your IP. Gradually increase your sending volume, typically by doubling it weekly or every few days, but always monitor your metrics closely. A typical warming period can range from a few weeks to a month or even longer for very high volumes.
Day
Target volume
Gmail (%)
Outlook (%)
Yahoo (%)
Other (%)
1
1000
50
15
15
20
2
2000
50
15
15
20
3
3000
50
15
15
20
4
4000
50
15
15
20
5
5000
50
15
15
20
Beyond volume, it's critical to consider the distribution of your emails across different ISPs. Instead of warming up for one ISP at a time, I recommend sending a mixed volume to a diverse set of domains. This diversified approach helps build a balanced reputation across the email ecosystem. A balanced approach gives all major ISPs a chance to assess your sending patterns.
Crafting your warming schedule
A robust IP warming strategy goes beyond just increasing volume. It integrates several best practices to ensure long-term deliverability. First, ensure your email list is clean and permission-based. Sending to unengaged or invalid addresses will quickly hurt your sender reputation, making it harder for your emails to reach the inbox. List hygiene is non-negotiable for successful warming and sustained performance.
Second, proper email authentication is paramount. This includes SPF, DKIM, and DMARC. These protocols verify that your emails are legitimate and prevent spoofing. Misconfigured authentication can lead to emails being rejected, regardless of your IP's reputation. Make sure these records are correctly set up before you start sending.
Finally, focus on sending high-quality, relevant content that your subscribers want to receive. This drives engagement, which is a key factor in building trust with ISPs. Monitor your engagement rates, open rates, click-through rates, and crucially, your spam complaint rates. High complaint rates are a red flag and can quickly land your IP on a blacklist (or blocklist). If you see a spike in complaints, slow down your sending and re-evaluate your strategy and list segmentation.
Maintaining reputation and scaling
Once you've warmed up your IP and reached your desired sending volume, the work isn't over. Maintaining a strong sender reputation requires ongoing effort. Consistency is key; try to send emails regularly and avoid large, infrequent blasts from your dedicated IP, as this can trigger ISP filters looking for unusual sending patterns. Your sending frequency should align with your subscribers' expectations.
Regularly cleaning your email list is also crucial. Remove inactive subscribers and bounces to maintain a healthy list. Unengaged recipients can quickly erode your sender reputation and increase your risk of hitting spam traps. A clean list ensures you're sending to genuinely interested recipients, leading to better engagement metrics and a positive sender score.
Best practices for maintaining reputation
Segment your audience: Send highly targeted content to engaged users.
Monitor feedback loops: Act quickly on spam complaints and remove users.
Provide clear opt-out options: Reduce spam complaints with easy unsubscribing.
For ongoing deliverability, continuous monitoring is non-negotiable. Keep a close eye on your deliverability metrics, including open rates, click rates, bounce rates, and spam complaint rates. Tools like ISP Postmaster Tools (like Google Postmaster Tools) provide invaluable insights into how ISPs perceive your sending. Pay attention to any sudden drops in inbox placement or increases in complaints, as these are indicators that you might need to adjust your sending strategy or clean your list further.
Key strategies for high-volume sending
When considering scaling your email volume, the choice between shared and dedicated IPs often arises. While shared IPs can be a good starting point for low-volume senders, dedicated IPs offer more control over your sender reputation, which is crucial for high-volume sending. With a dedicated IP, your reputation is solely based on your sending practices, giving you a clearer picture of your deliverability.
For very large sending volumes, it might be necessary to consider multiple dedicated IPs or even a pool of IPs. This strategy helps distribute your sending load and mitigate risks. If one IP encounters an issue, your entire sending operation isn't compromised. Implementing a system to rotate sending across these IPs or assign specific types of mail to certain IPs can optimize your deliverability.
Common scaling problems
Sudden volume spikes: Triggers ISP spam filters.
Inconsistent sending: Breaks established reputation.
Poor list hygiene: Leads to high bounces and complaints.
Continuous list cleaning: Implement a regular list hygiene routine.
Furthermore, if your email volume varies significantly throughout the year, such as seasonal peaks, plan your warming and scaling to accommodate these fluctuations. It's better to maintain a consistent baseline volume and gradually increase it for peak periods, rather than stopping and starting. This proactive approach helps ISPs maintain trust in your sending habits and keeps your emails out of the spam folder.
Advanced considerations for consistency
Beyond the technical aspects, understanding your audience's behavior is critical for scaling. Different recipient bases, especially large ones, might react differently to increased volume. Some might be more tolerant of higher frequencies, while others might quickly mark emails as spam if they feel overwhelmed. This is why list segmentation plays an even more important role when scaling.
When your volume grows, so does the impact of minor issues. A small percentage of bounces or complaints on a low volume can be negligible, but on a large scale, it can quickly lead to blocklists (or blacklists) and significant deliverability problems. Regularly review your email content, ensuring it's always relevant and provides value. Generic or irrelevant content is a fast track to disengagement and spam complaints.
Finally, be prepared to adapt. The email landscape is constantly evolving, with ISPs regularly updating their filtering algorithms. What worked yesterday might not work tomorrow. Staying informed about industry best practices, monitoring your metrics diligently, and being agile in your strategy are essential for long-term email deliverability success at any volume.
The journey to optimal deliverability
IP warming and email volume scaling are foundational elements of a strong email deliverability program. It’s a journey that requires patience, consistency, and a keen eye on your data. By prioritizing list quality, implementing robust authentication, gradually increasing your sending, and continuously monitoring your performance, you can build and maintain the sender reputation needed to ensure your messages consistently reach the inbox.
Views from the trenches
Best practices
Always start by sending emails to your most engaged subscribers to build a positive reputation quickly.
Segment your audience by ISP domain and gradually increase volume to each, ensuring a balanced warm-up across major providers like Google, Microsoft, and Yahoo.
Maintain consistent sending patterns after warming; avoid large, infrequent bursts of email to prevent triggering spam filters.
Implement automated feedback loops to quickly identify and address high bounce rates or spam complaints, and adjust your sending as needed.
Common pitfalls
Suddenly sending high volumes from a new IP, which almost guarantees immediate blacklisting and poor deliverability.
Not monitoring engagement rates (opens, clicks) during the warming phase, missing crucial signals about your sender reputation.
Failing to clean your email list before warming up, leading to high bounce rates and spam traps that damage your IP.
Ignoring ISP-specific sending limits or unique requirements, which can result in throttling or blocking.
Expert tips
Consider a dual-IP strategy where one IP handles highly engaged transactional emails and another handles marketing campaigns, especially for large senders.
Use email authentication protocols (SPF, DKIM, DMARC) not just for compliance, but as a proactive measure to signal legitimate sending to ISPs.
If migrating ESPs, leverage any existing sender reputation by integrating the new IP warming with a portion of your current sending volume if possible.
For extremely high volumes, distribute your sends across multiple dedicated IPs to diversify risk and improve overall throughput.
Marketer view
Marketer from Email Geeks says that different Email Service Providers (ESPs) have varied recommendations for IP warming, with some rate-limiting mail or blending dedicated and shared IP sends during the ramp-up.
2024-05-15 - Email Geeks
Marketer view
Marketer from Email Geeks says they typically map out warmings by doubling the daily send volume week over week, for example, from 1% in week one to 16% by week five.
Google and 
Microsoft to observe your sending behavior. They look for signs of legitimate sending, such as low bounce rates, low spam complaints, and high engagement (opens and clicks).
50
15
15
