How do I warm up a new subdomain for low volume B2B email sends?
Michael Ko
Co-founder & CEO, Suped
Published 26 Jun 2025
Updated 16 Aug 2025
7 min read
Warming up a new subdomain for B2B email sends, especially at a low volume, might seem counterintuitive. Many assume that if the main domain is established, its subdomains inherit the same reputation. However, this isn't always the case. Email service providers (ESPs) and mailbox providers (MBPs) often view subdomains as separate entities, requiring their own reputation building from the ground up. The process you're asking about is actually domain warming, not IP warming. While related, IP warming focuses on the sender's IP address reputation, whereas domain warming builds trust for your specific sending domain or subdomain. For low-volume B2B sends, the warming strategy can be more flexible than for high-volume consumer campaigns. Let's explore how to best approach this.
Why warming a new subdomain is essential
A subdomain, such as e.yourdomain.com, effectively starts with a neutral sender reputation in the eyes of most major mailbox providers. While it benefits from the established trust of your root domain, it doesn't automatically inherit a perfect score. Building its own positive sending history is essential to ensure your emails consistently reach the inbox.
The goal of warming is to gradually show mailbox providers that you are a legitimate sender sending desired content. This involves sending increasing volumes of email to engaged recipients over time. For low-volume B2B sends, the warming process is typically less stringent than for mass consumer mailings, but it's still a critical step.
It's a common misconception that low volumes negate the need for warming. Even if you're sending only a few thousand emails a month, a new subdomain still needs to establish trust. Skipping this step can lead to your emails being filtered to spam, getting placed on a blacklist (or blocklist), or even temporary blocks, hindering your B2B outreach efforts. Building up a positive reputation helps you avoid these issues and ensures better email deliverability.
Crafting your low-volume warming strategy
For low-volume B2B sends, a phased approach focusing on recipient engagement is crucial. You don't need the extensive, multi-week ramp-up schedules typically advised for high-volume marketing. Instead, you can compress the warming period.
Start with your most engaged contacts: Begin by sending to your most active customers or prospects. These are individuals who have recently opened or clicked your emails, indicating high engagement. This positive interaction signals good sender behavior to mailbox providers. Gradually expand to less engaged segments.
Shorten the ramp-up time: For a total list size under 5,000, and with infrequent sends (e.g., two emails per month), your initial warming can be condensed significantly, possibly over 2-3 days, rather than weeks. This is because mailbox providers are generally more lenient with very small, consistent senders. Your existing main domain's reputation will also provide some foundational trust.
Maintain consistent sending: Even with low volume, try to send emails regularly from the new subdomain once warming is complete. Inconsistent sending can cause your reputation to cool down, requiring you to restart parts of the warming process. You can understand how to warm up a new domain through various guides.
Here's an example of a condensed warm-up schedule for a low-volume B2B subdomain using your proposed segmentation:
Day
Audience Segment
Sending Volume (% of total list)
Notes
Day 1
Active Customers
Start with a small percentage (e.g., 10-20%) of your most active contacts.
Focus on high engagement to build initial positive signals.
Day 2 (Morning)
Active + Lapsing Customers
Gradually increase volume to include your lapsing customers.
Monitor deliverability metrics closely.
Day 2 (Afternoon)
Active + Lapsing + Lapsed Customers
Expand further to include lapsed customers who still show some engagement potential.
Ensure no significant spikes in complaints or bounces.
Day 3
Active + Lapsing + Lapsed + Heavily Lapsed Customers
Include your full list, but be cautious with heavily lapsed contacts.
Consider a re-engagement campaign for very old contacts before adding them to regular sends.
After this initial phase, continue to send consistently at your desired low volume. Remember, this schedule is for warming a *subdomain* when you're on a *shared IP* (as is common with ESPs like HubSpot for marketing sends). If you were on a dedicated IP, the volumes and duration would be significantly different.
Key factors for successful warming
Beyond the sending schedule, several elements contribute to a successful warm-up and long-term deliverability for your B2B subdomain.
Audience quality: Ensure your B2B contacts are genuinely interested and have a reason to receive your emails. High engagement, characterized by opens and clicks, is the most powerful signal of a good sender reputation. Avoid sending to purchased or unverified lists, as this can quickly lead to high bounce rates and spam complaints.
Content relevance and quality: Send valuable and relevant content that encourages positive engagement. Personalize your B2B communications where possible. Avoid generic or overly promotional language during the warming phase.
Monitor blocklists (blacklists): Keep an eye on your subdomain's standing with major blocklists (or blacklists). Being listed can severely impact deliverability.
The danger of cold email
For B2B, it's tempting to include a high percentage of cold outreach. However, if cold email (unsolicited email) makes up more than 10% of your total sending volume, it can start to disproportionately define your sender reputation. This means even if your legitimate marketing sends are well-received, the negative signals from cold outreach can drag down your overall deliverability. It's often better to send cold emails from a different, highly isolated subdomain, or even a completely separate sending domain, if your volumes are substantial.
Consistency is paramount, even with low volume. Mailbox providers value senders who send emails consistently over time, as this helps them build a reliable profile of your sending behavior. Erratic sending patterns can raise red flags, making your warming efforts less effective.
Monitoring and adjusting your strategy
Monitoring your subdomain's performance during and after the warm-up is crucial. Pay close attention to key metrics that indicate your sender reputation and deliverability health.
Deliverability metrics: Track open rates, click-through rates, bounce rates, and spam complaint rates. A low bounce rate and virtually zero spam complaints are good indicators of a healthy sending reputation. Pay attention to how many emails are landing in the inbox versus spam folders.
Feedback loops: Sign up for feedback loops (FBLs) with major mailbox providers like Outlook.com and Gmail. FBLs notify you when a recipient marks your email as spam, allowing you to remove them from your list and prevent further damage to your reputation. Google Postmaster Tools are an excellent resource for this.
If you notice a sudden drop in deliverability or an increase in complaints, pause your sending and investigate. This could indicate a problem with your list quality, content, or that you've tried to increase volume too quickly. Adjust your strategy as needed. Sometimes, this means re-engaging with your most active segment for a few days to rebuild positive signals.
Understanding your reputation score
Your sender reputation is dynamic. For low-volume B2B senders, it's easier to maintain a good reputation with consistent, high-quality engagement. However, even a few negative signals (like spam traps or complaints) can have a disproportionate impact due to the smaller overall volume. Regularly check your email domain reputation to stay informed.
Views from the trenches
Best practices
Segment your audience by engagement levels and target the most active contacts first during warming.
Ensure robust email authentication (SPF, DKIM, DMARC) is properly configured for your new subdomain.
Maintain consistent sending patterns once warming is complete, even if volumes are low.
Prioritize sending highly relevant and engaging content to foster positive recipient interactions.
Common pitfalls
Confusing IP warming with domain warming, which are distinct processes.
Sending too much cold email from a new subdomain, which can quickly damage reputation.
Neglecting to monitor deliverability metrics and feedback loops during and after warming.
Assuming low volume negates the need for any warming, leading to unexpected blocks.
Expert tips
For low-volume B2B on shared IPs, a condensed 2-3 day warming for up to 5k contacts can be sufficient.
If cold email constitutes more than 10% of your volume, it will likely define your sender reputation.
Separating marketing, transactional, and sales emails to different subdomains is a sound strategy.
Mailbox providers are more lenient with very small, consistent senders than large, erratic ones.
Expert view
Expert from Email Geeks says that for low volumes and infrequent sends, the standard multi-week IP warming plans might not be relevant, and a shorter, more flexible approach focusing on domain reputation is likely sufficient.
February 28, 2023 - Email Geeks
Expert view
Expert from Email Geeks says that sending 5,000 emails twice a month off a dedicated IP might make it difficult to ever truly warm the IP, as typical dedicated IP warming starts at much higher volumes.
February 28, 2023 - Email Geeks
Final thoughts on subdomain warming
Warming up a new subdomain for low-volume B2B email sends is a necessary step to establish and maintain a positive sender reputation. While the process is less intensive than for high-volume campaigns or dedicated IPs, it still requires a strategic approach. Focus on segmenting your audience, gradually introducing volume, ensuring strong email authentication, and vigilantly monitoring your deliverability metrics.
By prioritizing sending to your most engaged contacts first and maintaining consistent, quality content, you can quickly build trust with mailbox providers. This proactive approach helps you avoid common deliverability pitfalls, such as being placed on a blacklist (or blocklist), and ensures your valuable B2B communications consistently reach their intended recipients' inboxes.
HubSpot for marketing sends). If you were on a dedicated IP, the volumes and duration would be significantly different.
Outlook.com and 
Gmail. FBLs notify you when a recipient marks your email as spam, allowing you to remove them from your list and prevent further damage to your reputation. Google Postmaster Tools are an excellent resource for this.
