Why are my high open rates misleading during warm-up?

High open rates, especially those influenced by privacy features like Apple Mail Privacy Protection, can be misleading. Mailbox providers (MBPs) prioritize active engagement signals, such as clicks, replies, and emails being moved from spam to inbox. If these deeper engagement metrics are low, MBPs may still flag your emails as unwanted, leading to spam placement despite inflated open rates.

How long should a subdomain warm-up take?

A subdomain warm-up typically takes 2-6 weeks, but this can vary significantly based on your sending volume, list quality, and audience engagement. It's a gradual process of building trust with MBPs by consistently sending desired content to engaged recipients. Trying to rush it often backfires.

What are common hidden factors affecting new subdomain deliverability?

Hidden factors can include inherited negative reputation from your parent domain, associations with disreputable affiliates, or links within your emails that point to flagged websites. Even if your new subdomain is technically clean, these external factors can signal risk to MBPs.

Should I adjust my warm-up strategy if emails go to spam early on?

If emails start landing in spam early on, consider pausing your warm-up, re-evaluating your list segmentation (focusing on clickers, not just openers), reviewing all links for suspicious content, and verifying DNS authentication. Then, resume with an even more conservative volume increase and monitor closely for positive engagement.

What role do clicks play compared to opens during warm-up?

During warm-up, clicks play a much more significant role than opens in building sender reputation. Clicks demonstrate explicit user interest and engagement with your content, which is a strong positive signal to mailbox providers that your emails are desired. Opens, especially privacy-protected ones, are less indicative of true engagement.

Why are my emails going to spam folder during new subdomain warm up even with good open rates? - Troubleshooting - Email deliverability - Knowledge base

It is incredibly frustrating to experience emails landing in the spam folder, especially during a new subdomain warm-up, when your initial open rates look promising. You follow the best practices, ensure your DNS records are in place, and carefully segment your audience, yet a sudden drop into the spam abyss can leave you wondering what went wrong.

This scenario highlights a common misconception in email deliverability: open rates alone are not a complete indicator of success, especially for a nascent sending identity. While a high open rate seems positive, mailbox providers (MBPs) like

Gmail and

Outlook look for a broader range of engagement signals to build trust for a new sender. This becomes even more critical when warming a new subdomain, as there is no established history to rely on.

The challenge is that while your initial warm-up volumes might seem low to you, they are still significant enough for sophisticated spam filters to begin forming an opinion. If other critical factors are out of alignment, or if deeper engagement signals are missing, these systems can quickly flag your new sending identity as suspicious, regardless of how many people open the email. Let's delve into why this happens and what can be done to get your emails back into the inbox.

The deceptive nature of open rates during warm up

The primary issue with relying solely on open rates during warm-up is the evolution of email privacy features, such as Apple Mail Privacy Protection. These features can automatically load tracking pixels, registering an open even if the recipient hasn't truly viewed or engaged with your email. This can create a false sense of security, showing inflated open rates that don't reflect actual user interest.

MBPs (Mailbox Providers) like

Yahoo and Google are less concerned with passive opens and more interested in explicit positive engagement. This includes clicks on links within the email, replies, forwards, adding the sender to contacts, or moving an email from the spam folder to the inbox. For a new subdomain, these stronger signals are vital for building a positive reputation. If you have high opens but low (or zero) clicks, MBPs interpret this as a lack of true interest in the content, which can lead to spam folder placement despite the seemingly good open rates. You can review Google's sender guidelines for more information on how they evaluate senders.

When the volume of emails from a new subdomain suddenly increases, even if starting from a small base, MBPs scrutinize the sending behavior closely. If the positive engagement signals, particularly clicks, do not match the increasing volume, filters can quickly assume the mail is unwanted, pushing it to the spam folder. This is why some emails go to Gmail spam even with good authentication and high open rates.

Beyond the warming schedule: hidden reputation factors

While a consistent and gradual warm-up schedule is foundational, it is often just one piece of a complex puzzle. Even if your warm-up schedule has proven successful in the past, changes in MBP algorithms and stricter filtering practices mean that what worked yesterday might not work today. This is particularly true for

Microsoft and Google, which continuously adapt their anti-spam measures.

Typical warm-up strategy

Gradual volume increase over time, typically doubling send volume every few days, starting with highly engaged segments.

Assumptions during warm up

Opens mean engagement: A high open rate is often assumed to be sufficient for reputation building during initial sends.
Volume is the only factor: If the volume increase is slow, it is believed to be safe, regardless of other signals.

Mailbox provider perspective

MBPs assess numerous signals beyond just volume and opens. They seek explicit positive engagement to build trust in a new sending domain or subdomain.

Hidden factors for spam placement

Low active engagement: If clicks, replies, or inbox moves are low relative to opens, it suggests emails are not truly wanted.
Subdomain associations: The new subdomain might inherit negative reputation from the root domain's history, or from problematic links within the email.
Shared IP issues: Even with a dedicated sending domain, underlying shared IPs (if used by your ESP) can influence deliverability if other senders on them are problematic.

Hidden reputation factors often stem from past activities linked to your primary domain or any associated entities. For instance, linking to websites that have a poor reputation, or unknowingly associating with affiliates known for spammy practices, can significantly damage your new subdomain's standing. Even if the subdomain itself is new, the MBPs are sophisticated enough to connect the dots and attribute existing negative scores, causing emails to go to spam during ESP migration or warm-up.

Warning: Beware of external links

Always audit all links within your emails, especially during warm-up. Ensure they point to reputable domains and are not associated with known spammers or sites flagged for security issues. Even if your content is clean, a single problematic link can trigger spam filters and ruin your sending reputation on a new subdomain.

It is crucial to consider the broader context of your domain's historical reputation and any external elements that could influence it. MBPs maintain detailed records of domain and IP behavior. If there's any perceived link to past questionable activities, your new subdomain will face an uphill battle. This is why it’s important to continually improve your domain reputation by addressing any historical baggage or problematic associations.

Content and recipient engagement signals

Beyond technical configurations and volume, the actual content of your emails and how recipients interact with it are paramount. During warm-up, sending highly engaging content to your most active subscribers is non-negotiable. This means not just focusing on those who opened your past emails, but specifically those who clicked links, replied, or made purchases.

MBPs use a range of engagement metrics to determine where to place your emails. A high open rate combined with a low click-through rate, for example, can be a negative signal. It suggests that while the email might have been technically delivered, the content wasn't compelling enough to elicit a positive action. For new subdomains, this lack of active engagement can prevent the necessary trust from building. Learn more about how to increase your email click-through rate.

Metric	Why it matters during warm-up
Open rate	Historically a key metric, but less reliable now due to privacy features like Apple Mail Privacy Protection. Can be inflated and doesn't always reflect true engagement. Refer to this article on why high open rates don't always help.
Click-through rate (CTR)	A strong indicator of genuine interest. MBPs highly value clicks as they show recipients are actively engaging with your content.
Spam complaints	Even a small number can be detrimental during warm-up. Monitor closely and aim for zero.
Inbox moves	When recipients manually move your email from the spam folder to the inbox, it sends a powerful positive signal to MBPs, indicating the mail is wanted.

The balance between send volume and genuine engagement is delicate. If you increase volume too quickly without sufficient positive engagement signals, it can quickly backfire, causing your emails to be filtered to spam. This is a common reason emails from new domains go to spam, even with seemingly low sending volumes.

Technical foundation and the real impact of blacklists (blocklists)

Before even considering content or volume, your technical setup must be flawless. Ensure your SPF, DKIM, and DMARC records are correctly configured for your new subdomain. Any misconfiguration here can immediately flag your emails as suspicious, regardless of how good your engagement metrics appear. A single typo or misstep in these DNS records can negate all your warm-up efforts.

Example DMARC record to checkDNS

v=DMARC1; p=none; rua=mailto:reports@yourdomain.com; ruf=mailto:forensic@yourdomain.com; fo=1;

Another critical area is monitoring for blacklists (or blocklists). While a brand new subdomain should ideally start clean, it is possible for it to be placed on certain email blacklists (blocklists) if initial sends trigger spam traps or generate a high volume of complaints that are not reported back to you via standard feedback loops. Some blocklists operate on a low-threshold basis, and getting listed even briefly can damage your reputation.

Finally, ensure you are leveraging tools like

Google Postmaster Tools to monitor your domain reputation with key MBPs. While it might not provide granular complaint data for very low volumes, it offers invaluable insights into your spam rate, IP and domain reputation, and authentication errors, helping you pinpoint issues quickly and effectively. Be aware that the spam rate threshold for reporting in Postmaster Tools is not published, meaning low volumes might not show immediate complaint data.

Views from the trenches

Best practices

Start with the most engaged segment of your list, based on recent clicks, not just opens.

Increase send volume very gradually, perhaps 10-20% per day, rather than doubling.

Focus on driving active engagement like clicks, replies, and inbox moves during warm-up.

Regularly check your DMARC reports for authentication failures and potential issues.

Common pitfalls

Over-reliance on open rates as a primary metric during new subdomain warm-up.

Ignoring historical reputation issues of the parent domain or linked external sites.

Being too aggressive with send volume increases, even from a small starting point.

Not monitoring for bounces and spam complaints from all available feedback loops and tools.

Expert tips

Monitor your domain's health with tools that provide detailed insights into your reputation.

Consider a short pause and restart of your warm-up if you hit a spam wall early on.

Segment your audience based on last clicked engagement rather than last opened.

Carefully vet all links in your emails to ensure they don't point to suspicious domains.

Marketer view

Marketer from Email Geeks says open rates alone do not significantly influence mailbox providers. They need to see positive engagement signals to determine if the mail is wanted by recipients.

2022-04-13 - Email Geeks

Expert view

Expert from Email Geeks says that even a schedule of doubling volumes, while seemingly conservative, can still be too aggressive for modern mailbox providers like Gmail, suggesting a slower ramp-up is often necessary.

2022-04-13 - Email Geeks

Navigating deliverability in the modern email landscape

Experiencing emails going to spam during a new subdomain warm-up, even with seemingly good open rates, is a challenging but common deliverability issue. It underscores the fact that modern email deliverability is about much more than just opens or basic authentication. It requires a holistic approach that considers active engagement signals, the underlying reputation of your domain and its associations, and meticulous technical configuration. For further reading, check out our guide on why your emails go to spam.