Warming up a new subdomain for email sending is a critical step to ensure your messages reach the inbox, rather than landing in spam or being blocked. While you might have an established reputation on your root domain, a subdomain is often treated as a distinct entity by mailbox providers, meaning it needs its own reputation built from the ground up. This process is similar to warming up a completely new domain, although an existing good IP reputation can sometimes provide a slight advantage.
The goal is to gradually introduce the new subdomain to mailbox providers, demonstrating consistent, positive sending behavior. This helps them trust your sending practices and allocate a good sender reputation to your new subdomain. Ignoring this step can lead to significant deliverability issues, including emails being deferred, junked, or even outright blocked, impacting your outreach and engagement.
Why warm up a subdomain?
Even if your primary domain has an excellent sending history, its reputation does not automatically transfer to a new subdomain. Mailbox providers, such as Google, often assign unique reputation scores to each subdomain, even if they share the same root domain. This distinct evaluation means that a fresh subdomain starts with little to no reputation, necessitating a dedicated warm-up.
The main benefit of using a subdomain for email sending is to isolate different mail streams. For instance, you might use one subdomain for marketing emails (e.g., marketing.yourdomain.com) and another for transactional emails (e.g., trans.yourdomain.com). This separation protects your primary domain's reputation. If one stream encounters issues, like a high spam complaint rate, it won't negatively impact the deliverability of your other, more critical email types.
A proper warm-up process builds trust with internet service providers (ISPs). They analyze your sending patterns, including volume, frequency, and recipient engagement. By starting small and gradually increasing your volume, you signal that you are a legitimate sender, which is crucial for achieving high inbox placement rates and avoiding various email deliverability issues.
Benefits of warming up a subdomain
Reputation Isolation: Protect your main domain from deliverability issues specific to certain email campaigns, such as cold outreach or bulk marketing.
Improved Deliverability: Build a positive sender reputation for the specific subdomain, leading to better inbox placement for its designated email type.
Enhanced Monitoring: Gain clearer insights into the performance and reputation of specific email flows through dedicated metrics and domain warm-up reports.
Compliance: Adhere to new sender requirements from major providers that emphasize reputation-building.
Preparing for subdomain warm-up
Before you begin sending from your new subdomain, proper email authentication is non-negotiable. This includes SPF, DKIM, and DMARC. These protocols verify that you are authorized to send emails from your domain, a fundamental factor in building sender trust. Ensuring these records are correctly configured for your subdomain is the first technical hurdle to clear.
SPF record example for a subdomain
v=spf1 include:_spf.example.com ~all
Another crucial aspect is audience selection. During the warm-up phase, you should send to your most engaged and active subscribers. These are recipients who are highly likely to open, click, and reply to your emails, sending positive signals to ISPs. Avoid sending to cold, unengaged, or questionable lists, as this can quickly damage your new subdomain's reputation and potentially land you on a blacklist or blocklist.
The content of your emails also plays a significant role. Send valuable, relevant, and expected content that encourages engagement. Avoid anything that could be perceived as spammy, such as overly promotional language, excessive images, or broken links. Consistent, high-quality content helps reinforce positive sender behavior.
New cold domain warm-up
Warming up a new, completely cold domain is typically a longer, more cautious process. You start with very low volumes (e.g., 50-100 emails per day) and gradually increase, focusing heavily on engagement metrics from the outset. The absence of any prior history means ISPs are highly scrutinizing.
Reputation: Zero existing reputation, builds from scratch.
Timeframe: Can take several weeks to months, depending on target volume.
Risk: Higher risk of initial blocking or spam folder placement.
Subdomain warm-up on warm IP
When warming a subdomain on an already warmed IP address, the process can often be smoother than with a completely new domain. While the subdomain's reputation is distinct, the established IP reputation provides a foundational level of trust. This means you might be able to start with slightly higher volumes or ramp up a bit more quickly, but caution is still essential.
Timeframe: Potentially faster warm-up than a cold domain, but still requires patience.
Risk: Lower initial risk due to warm IP, but subdomain reputation can still be damaged.
Executing the warm-up schedule
The core of subdomain warm-up is a gradual increase in sending volume. There isn't a one-size-fits-all schedule, as it depends on your specific sending volume and target audience. However, a common approach is to start with a very low volume, typically 50-100 emails on day one, and then incrementally increase the volume each day or week. The rate of increase should be conservative, perhaps 10-15% daily, especially in the initial phases.
During the warm-up, focus on sending to highly engaged subscribers first. These are contacts who have recently opened or clicked your emails. Their positive engagement signals trust to ISPs. As your subdomain's reputation grows, you can gradually expand to broader segments of your list. Remember, quality over quantity is key, especially in the early stages.
Consistency is also vital. Try to send emails daily or at least consistently throughout the week, even if the volumes are small. Irregular sending patterns can raise red flags with mailbox providers. Maintain a steady cadence to build a predictable and positive sending history for your new subdomain, which is critical for long-term email deliverability.
Day
Volume Sent
Day 1-3
50-100 emails/day to most engaged contacts
Day 4-7
100-250 emails/day, expand to slightly less engaged
Week 2
250-500 emails/day, continue gradual expansion
Week 3-4
500-1,000+ emails/day, broadening audience
Beyond
Gradually increase by 10-15% daily/weekly towards target volume
Monitoring and adjusting
Monitoring your subdomain's performance throughout the warm-up is crucial. Pay close attention to key metrics such as open rates, click-through rates, bounce rates, and crucially, spam complaint rates. A sudden increase in bounces or complaints is a clear sign that you might be ramping up too quickly or sending to an unengaged audience.
Utilize Google Postmaster Tools (GPT) for insights into your domain's reputation with Gmail, including spam rates and IP/domain reputation scores. Also, keep an eye on various email blocklists (or blacklists) to ensure your new subdomain isn't listed. Early detection allows you to adjust your strategy and prevent further damage.
Be prepared to adjust your sending volume and strategy based on the feedback you receive. If you notice a dip in deliverability, reduce your sending volume and reassess your list quality and content. A successful warm-up isn't about rushing to max volume, but about patiently building a robust and trusted sender reputation.
Common pitfalls to avoid
Rushing the Process: Increasing volume too quickly is the most common mistake, leading to immediate deliverability issues.
Ignoring Engagement: Sending to unengaged contacts or purchased lists can swiftly damage your new reputation. Using unverified lists also leads to spam traps.
Inconsistent Sending: Erratic sending patterns make it difficult for ISPs to gauge your legitimacy.
Poor Content: Sending low-quality or spammy content will result in higher complaint rates and blocklistings.
Final thoughts on subdomain warm-up
Transitioning to a new subdomain for email sending is a strategic move that can significantly enhance your email program's resilience and deliverability. While it requires a deliberate warm-up process, the benefits of reputation isolation and improved sender trust are invaluable.
By diligently setting up authentication, carefully managing your sending volume to engaged audiences, and continuously monitoring your performance, you can successfully warm up your subdomain. This methodical approach will ensure your emails consistently reach the inbox, safeguarding your overall email marketing efforts.
Views from the trenches
Best practices
Gradually change out the domain for email sending while still using all the existing IPs to leverage their reputation.
Test a percentage of your mail stream, keeping the existing DKIM signing configuration, to determine the next course of action.
Introduce the new subdomain as an additional DKIM signature on messages to start building its reputation without being too disruptive.
Common pitfalls
Do not assume that the root domain's reputation will automatically carry over to subdomain variations, as many receivers treat them independently.
Avoid starting the warming process from scratch with existing warm IPs if you are transitioning to a new subdomain; leverage the IP reputation.
Don't overlook the impact of sibling domain activity, as it can affect a subdomain's deliverability even if the subdomain has a good Google Postmaster Tools reputation.
Expert tips
IP reputation remains a crucial factor when evaluating domain reputation, even if subdomains receive independent scores.
Domain transitions from parent to subdomain generally proceed more smoothly than introducing a completely cold domain.
The warm-up schedule and its effectiveness are highly variable depending on the receiver or mailbox provider.
Marketer view
Marketer from Email Geeks says they would start by gradually changing out the domain, while still utilizing all existing IPs, as the warming process mainly applies to the domain in this scenario, not the IPs.
2022-09-20 - Email Geeks
Marketer view
Marketer from Email Geeks says it depends on the methods the receiver uses, as some treat second-level domains differently than third-level domains, or treat them independently.
Google, often assign unique reputation scores to each subdomain, even if they share the same root domain. This distinct evaluation means that a fresh subdomain starts with little to no reputation, necessitating a dedicated warm-up.
new sender requirements from major providers that emphasize reputation-building.
Gmail, including spam rates and IP/domain reputation scores. Also, keep an eye on various email blocklists (or blacklists) to ensure your new subdomain isn't listed. Early detection allows you to adjust your strategy and prevent further damage.
