Do I need to warm up my email list of 100k contacts?
Matthew Whittaker
Co-founder & CTO, Suped
Published 25 Jun 2025
Updated 19 Aug 2025
8 min read
The question of whether to warm up an email list of 100,000 contacts is a common one, especially when you're preparing to send a high volume of emails. Many factors influence this decision, and it's not always a straightforward yes or no. It largely depends on the history of your sending infrastructure, the nature of the list itself, and your specific email service provider (ESP).
While the term "warm up" is often associated with a new IP address or a new sending domain, the principle of gradually increasing email volume can also apply to a large, unengaged, or dormant contact list. This helps build a positive sender reputation with mailbox providers, preventing your emails from landing in spam folders.
For a list of 100k contacts, taking a cautious approach is generally recommended to safeguard your deliverability. A sudden surge in volume to a new or unengaged audience can trigger spam filters, leading to low inbox placement rates and potentially getting your domain or IP blacklisted (or blocklisted).
Understanding the need for warm-up
Before deciding on a warm-up strategy, it's crucial to understand the nuances of your situation. The need for warming up a 100k contact list hinges on several key factors, primarily revolving around your sender history and the list's engagement.
The primary reasons to warm up typically relate to the sending infrastructure, rather than just the list size alone. If you're using a new IP address or a new sending domain, a warm-up is almost always necessary to build a positive sender reputation. This process involves sending small volumes of emails initially and gradually increasing them over time to demonstrate legitimate sending behavior to mailbox providers. This is important even with a shared IP, especially if you're a new sender.
However, the characteristics of your 100k list are equally important. If it's a cold email list, has not been used in a long time, or was acquired without proper opt-in, it carries significant risk. Sending to such a list without preparation can lead to high bounce rates, spam complaints, and low engagement, all of which harm your sender reputation and can get your domain or IP blocklisted.
Strategic warm-up for large lists
If you determine that a warm-up is necessary for your 100k list, a strategic approach is vital. The goal is to introduce your sending volume gradually to mailbox providers while minimizing negative feedback.
Segmenting your list for warm-up
Start by segmenting your 100k list based on engagement. Identify your most active and engaged contacts first. These are the individuals most likely to open your emails, click links, and interact positively. Sending to them first helps establish a positive rapport with mailbox providers, showing that your emails are valued.
For the initial sends, target a small, highly engaged subset, perhaps 1,000 to 5,000 contacts. Monitor your metrics closely, looking for good open rates, click-through rates, and minimal bounces or complaints. If these initial sends perform well, you can gradually increase the volume over successive sends, incorporating less engaged segments of your list.
Gradual volume increase
The progression for warming up a large list should be methodical. A common strategy involves doubling your send volume every few days, assuming positive engagement. For a 100k list, this could mean starting with 1k-5k, then 10k, then 20k, and so on. This gradual increase helps build trust with internet service providers (ISPs) like Gmail and Outlook, signalling that you are a legitimate sender.
Start small: Send to the most engaged 1,000 to 5,000 contacts.
Monitor performance: Track open rates, click-through rates, and bounce rates.
Gradually scale: Increase volume by 20-50% daily or every few days if performance remains strong.
Prioritize engagement: Continue to send to your most active contacts first as you scale up.
Other deliverability best practices
While warming up your sending infrastructure or an old list is key, several other best practices significantly impact your email deliverability, especially when dealing with a large contact base. Ignoring these can undermine even the best warm-up efforts, leading to emails being sent to spam or getting your domain placed on a blocklist (or blacklist).
Maintain list hygiene
Regularly cleaning your email list is paramount. Remove inactive subscribers, hard bounces, and any addresses that haven't engaged in a significant period. Sending to a clean, engaged list improves your sender reputation and reduces the likelihood of hitting spam traps, which are designed to catch senders with poor list management practices. You can learn more about how to develop a valuable email list from community insights.
Implement strong email authentication
Ensure your email authentication protocols, such as SPF, DKIM, and DMARC, are correctly configured. These records verify that your emails are legitimate and prevent spoofing. Properly configured DMARC, for instance, tells receiving servers how to handle emails that fail authentication checks, significantly impacting your deliverability and protecting your domain reputation. If you need assistance, our free DMARC record generator can help you create one.
Monitor your sender reputation
Continuously monitor your sender reputation. Tools like Google Postmaster Tools provide insights into your domain and IP reputation, spam rates, and delivery errors. Staying on top of these metrics allows you to identify and address issues promptly. Regularly checking if your IP or domain is on any email blocklists (or blacklists) is also crucial. Understanding how email blacklists work can help you react quickly if you find yourself listed.
New IP/domain or dormant list
If you are starting with a brand new IP address or a recently registered domain, warming up is essential. Similarly, if your 100k contact list hasn't been mailed in over 6-12 months, or was acquired through less-than-ideal means, a warm-up strategy is highly advisable. This prevents sudden spikes in volume that can trigger spam filters and lead to deliverability issues.
Objective: Build a positive sender reputation from scratch or rebuild trust with mailbox providers.
Risk: High risk of emails going to spam or domain/IP blacklisting (or blocklisting).
Engaged and active list
If your 100k contacts are highly engaged, regularly receive emails from you, and have explicitly opted-in, a traditional warm-up might not be necessary. Your existing sender reputation, built on consistent positive engagement, often allows you to send to your full list without drastic measures. However, even with an engaged list, large jumps in volume should be approached with caution.
Objective: Maintain existing positive sender reputation and avoid sudden spikes.
Risk: Lower risk, but still possible deliverability issues if volume scales too quickly.
Consider your ESP's capabilities
Many email service providers (ESPs) offer features to assist with warm-up processes, especially for dedicated IP addresses. If you're using a robust ESP, it's worth exploring their capabilities.
Leveraging ESP features
Some ESPs, particularly those used for high-volume sending like Mailgun, SparkPost, or even enterprise-level HubSpot Marketing Enterprise, offer automated or guided IP warming processes. These features are designed to manage the gradual increase in sending volume for new IPs, helping to build a good reputation. However, even with automation, vigilance is required. It is important to know if IP warmup is necessary when moving between ESPs.
Even if your ESP automates the IP warm-up, understanding the underlying principles and actively monitoring your campaigns is crucial. A large jump in volume still carries risk, so always be ready to pause or adjust your sending strategy if you observe a decline in deliverability metrics, such as increased bounce rates or spam complaints. This proactive monitoring is key, especially if you have a massive list like 100k contacts.
Final considerations
The decision to warm up your 100k email list isn't just about the size. It's about mitigating risk and ensuring your emails reach the inbox. By understanding the context of your list and your sending infrastructure, you can make an informed decision that protects your sender reputation.
Ultimately, a cautious and data-driven approach is best. Prioritize sending to your most engaged segments first, monitor your metrics diligently, and implement robust email authentication. These steps will help ensure that your large-scale email campaigns are successful and maintain high inbox placement rates.
Views from the trenches
Best practices
Always start sending to the most engaged segment of your list first.
Segment your 100k list by engagement levels for a controlled warm-up.
Regularly clean your email list to remove inactive subscribers and hard bounces.
Ensure SPF, DKIM, and DMARC are properly configured for all sending domains.
Continuously monitor your sender reputation using tools like Google Postmaster Tools.
Common pitfalls
Sending to an entire 100k list at once, especially if it's new or unengaged.
Ignoring high bounce rates or spam complaints during initial sends.
Neglecting list hygiene, which leads to hitting spam traps and reduced deliverability.
Failing to properly configure email authentication protocols, weakening sender trust.
Not monitoring your sender reputation, missing early signs of deliverability issues.
Expert tips
For a new sending IP or domain, gradual volume increase is crucial regardless of list size.
If your list is consent-based and regularly engaged, list warm-up may not be strictly necessary.
If your ESP offers automated IP warming, utilize it but continue to monitor performance closely.
Always be ready to reduce sending volume if you see negative metrics during a campaign.
The age and source of your list are critical factors in determining warm-up necessity.
Marketer view
A marketer from Email Geeks says to send to 1,000 contacts first, and if that goes well, then increase to 10,000 contacts to confirm positive reception before scaling further.
2021-06-08 - Email Geeks
Marketer view
A marketer from Email Geeks says if the contacts are consent-based and frequently mailed, a list warm-up should not be necessary; an A/B split test might be sufficient.
2021-06-08 - Email Geeks
The bottom line on warming up large email lists
Whether you need to warm up a 100k email list depends on the specifics of your sending environment and the list itself. If you're using a new IP or domain, or if the list is old, unengaged, or of unknown origin, a warm-up is highly recommended to protect your sender reputation and ensure deliverability.
However, if your 100k contacts are highly engaged and you have a consistent sending history, a formal warm-up might be less critical. In either case, always proceed with caution, monitor your metrics diligently, and adhere to best practices for email authentication and list hygiene to maintain strong deliverability.
Gmail and 
Outlook, signalling that you are a legitimate sender.
HubSpot Marketing Enterprise, offer automated or guided IP warming processes. These features are designed to manage the gradual increase in sending volume for new IPs, helping to build a good reputation. However, even with automation, vigilance is required. It is important to know if IP warmup is necessary when moving between ESPs.
