Why are Postmark transactional emails suddenly landing in Gmail spam?
Michael Ko
Co-founder & CEO, Suped
Published 5 May 2025
Updated 18 Aug 2025
7 min read
I've been seeing an unsettling trend lately, with perfectly legitimate transactional emails from Postmark suddenly finding their way into Gmail's spam folders. This isn't just a minor blip for one domain; it seems to be affecting multiple projects simultaneously, across different industries, even for senders who have had a flawless record for years. It's incredibly frustrating when your critical emails, like password resets, order confirmations, or account notifications, fail to reach the inbox.
When a major email service provider like Postmark experiences a widespread deliverability issue with a giant like Gmail, it signals that something significant has shifted. This often points to changes in recipient mailbox provider filtering algorithms or, in some cases, an underlying issue with the sending infrastructure itself. While Postmark is known for its robust deliverability, no provider is immune to these complex challenges.
The sudden shift in deliverability
When I first noticed the problem, it wasn't just a hunch. My inbox placement monitoring service immediately flagged a significant drop. This was then corroborated by reports from my quality assurance team, confirming that even their test emails were landing in spam at Gmail. This consistency across different projects using the same sender, Postmark, strongly suggested a broader issue rather than isolated incidents.
Shortly after, I saw reports surfacing on platforms like Reddit, with other senders experiencing the exact same sudden dip in Postmark deliverability, particularly to Gmail. This collective experience quickly turned individual concerns into a shared problem, indicating a systemic challenge.
This kind of widespread issue often points to either a significant change in Gmail's spam filtering criteria or a temporary hiccup on Postmark's side affecting their shared IP reputation with Gmail. In this scenario, it was confirmed to be a known issue by Postmark's support team, with an update eventually posted on their status page confirming increased Gmail spam reports. The swift confirmation from the service provider is crucial for understanding the scope of the problem.
Decoding the problem: what Gmail looks for
Gmail's filtering algorithms are incredibly sophisticated, constantly adapting to combat unwanted email. They analyze a multitude of factors to determine whether an email belongs in the inbox or the spam folder. When transactional emails, which are typically expected and often have high engagement, start landing in spam, it's a serious red flag. Key factors include sender reputation, authentication, and user engagement metrics.
Sender reputation is paramount. Gmail tracks your domain and IP reputation, categorizing it as high, medium, low, or bad. A sudden influx of complaints, even for a short period, can rapidly degrade this reputation. Conversely, consistent positive engagement helps maintain a strong standing. Understanding how to interpret your Google Postmaster Tools data is vital for diagnosing such issues.
Beyond reputation, strong email authentication is non-negotiable. This includes correctly configured SPF, DKIM, and DMARC records. While the initial report in this case indicated no issues with these, any misconfiguration or recent changes could impact deliverability. Google's new sender requirements for 2024 emphasize strict authentication for all senders, especially those sending more than 5,000 emails per day.
Understanding new Gmail and Yahoo requirements
Both Gmail and Yahoo have introduced new sender requirements that heavily impact deliverability, especially for bulk senders. Key mandates include: strict email authentication (SPF, DKIM, DMARC), a spam complaint rate below 0.1%, and easy one-click unsubscribe options. Failing to meet these can result in emails being rejected or sent straight to the spam folder. These changes highlight the need for robust email security and deliverability practices.
Common causes beyond a service-wide outage
Even if a service provider identifies a widespread technical glitch, it's important to remember that individual sending practices can exacerbate the problem or prevent a quick recovery. While Postmark was addressing a global Gmail issue, senders should still review their own internal processes. For instance, a poor email list can quickly lead to deliverability problems, regardless of the sending platform.
One common pitfall is a sudden, unmanaged increase in email volume. If you abruptly start sending a large number of emails, even transactional ones, mailbox providers might flag them as suspicious. This is where proper email warming can be beneficial, gradually building up sender reputation. However, for a sudden, unexplained drop affecting many users, it is more likely an external factor, though volume spikes can still be a contributing factor on an individual account basis.
High spam complaint rates are another major contributor to inbox placement issues. Even for transactional emails, if recipients mark them as spam, it sends a strong negative signal to mailbox providers. This can happen if the emails are irrelevant, unexpected, or if users simply don't remember opting in. Monitoring feedback loops can help identify sources of complaints.
Proactive steps
Monitor constantly: Use tools and Postmaster data to track deliverability metrics.
List hygiene: Regularly remove inactive subscribers and hard bounces.
Authentication: Ensure SPF, DKIM, and DMARC are always correctly configured.
Reactive measures
Diagnose quickly: Use detailed reports to pinpoint the source of deliverability issues.
Content review: Adjust email content to avoid spam triggers after an issue.
Remediation: Delist from blacklists (or blocklists) and warm up IPs if necessary.
Actionable steps to restore inbox placement
When facing deliverability challenges, proactive monitoring and quick action are essential. The first step is to diligently monitor your metrics, especially within Google Postmaster Tools. Look for anomalies in your spam rate, IP reputation, and domain reputation. A sudden spike in spam complaints or a drop in reputation scores can indicate a serious problem that needs immediate attention. You can find more details on how to use Postmaster Tools for domain reputation management.
Regularly auditing your email content for anything that might trigger spam filters is also crucial. This includes avoiding spammy keywords, excessive images, or broken links. Ensure your transactional emails are concise, clear, and directly relevant to the user's action. Personalized and expected content generally performs better.
Finally, maintaining a clean and engaged email list is fundamental. Remove inactive subscribers and hard bounces regularly. Be vigilant about spam traps, which can seriously damage your sender reputation and lead to blacklisting (or blocklisting) if you hit them. If you suspect you're on a blocklist, use a blocklist checker to investigate. For a deeper understanding, explore an in-depth guide to email blocklists.
Views from the trenches
Best practices
Always monitor your Google Postmaster Tools data closely for any sudden changes in domain or IP reputation, or spam rates.
Ensure all your sending domains have properly configured authentication protocols, including SPF, DKIM, and DMARC.
Regularly clean your email lists to remove inactive users and reduce the chance of hitting spam traps.
Implement a system for tracking user engagement with your transactional emails, as low engagement can negatively affect deliverability.
Have a clear escalation path with your email service provider's support for critical deliverability issues.
Common pitfalls
Failing to check Google Postmaster Tools after a sudden drop in inbox placement means you are missing critical diagnostic data.
Assuming authentication is perfect without regular checks, especially with changing provider requirements, can lead to deliverability failures.
Not segmenting transactional email traffic from marketing email traffic can mix reputations and cause issues for critical messages.
Ignoring recipient feedback loops and high spam complaint rates can quickly degrade your sender reputation with mailbox providers.
Waiting too long to contact your email service provider's support or publicizing the issue can delay resolution.
Expert tips
Leverage DMARC reports to gain granular visibility into your email authentication status and identify potential issues.
Understand that even transactional email streams can be impacted by reputation issues, especially from shared IP pools.
Pay close attention to subtle changes in email service provider policies, as these can suddenly impact deliverability.
If using a shared IP, remember that the actions of other senders can affect your deliverability, making continuous monitoring essential.
Consider the impact of reverse DNS (rDNS) records; an incorrect configuration can severely harm deliverability.
Marketer view
Marketer from Email Geeks says they noticed the same deliverability issue for broadcast streams, and then it started affecting transactional emails as well.
2025-03-24 - Email Geeks
Marketer view
Marketer from Email Geeks says they received a warning in their Postmark account regarding the issue.
2025-03-24 - Email Geeks
Navigating deliverability challenges
While a sudden, widespread issue like Postmark transactional emails landing in Gmail spam can be alarming, it often stems from either a temporary technical glitch on the provider's end or a shift in mailbox provider policies. Staying informed through status pages and community discussions is crucial during such events. However, consistent vigilance over your own sending practices remains the cornerstone of good email deliverability.
Maintaining excellent sender reputation, ensuring robust email authentication, and managing your recipient lists proactively are not just best practices, but necessities in today's email landscape. Even after a major incident is resolved, the impact on your reputation might linger, requiring sustained effort to restore full inbox placement. Ongoing monitoring and a responsive strategy are key to navigating the ever-evolving world of email deliverability.
Postmark experiences a widespread deliverability issue with a giant like Gmail, it signals that something significant has shifted. This often points to changes in recipient mailbox provider filtering algorithms or, in some cases, an underlying issue with the sending infrastructure itself. While Postmark is known for its robust deliverability, no provider is immune to these complex challenges.
Gmail and 
Yahoo have introduced new sender requirements that heavily impact deliverability, especially for bulk senders. Key mandates include: strict email authentication (SPF, DKIM, DMARC), a spam complaint rate below 0.1%, and easy one-click unsubscribe options. Failing to meet these can result in emails being rejected or sent straight to the spam folder. These changes highlight the need for robust email security and deliverability practices.
