Why are marketing emails going to Gmail spam despite passing authentication checks?
Michael Ko
Co-founder & CEO, Suped
Published 22 Jun 2025
Updated 18 Aug 2025
8 min read
It can be incredibly frustrating to see your marketing emails consistently landing in Gmail's spam folder, especially when all your authentication checks, like SPF, DKIM, and DMARC, show a clear PASS. I've heard this story countless times, where the technical setup appears flawless, yet inbox placement remains elusive. It feels like you've done everything right on the authentication front, but Gmail's filters still see your messages as unwanted.
The reality is that while email authentication is crucial for proving your identity and preventing spoofing, it's just one piece of a much larger puzzle. Gmail, like other major mailbox providers, employs sophisticated algorithms that evaluate numerous factors beyond just SPF, DKIM, and DMARC. These systems are designed to protect users from unwanted mail, and sometimes, legitimate marketing messages can get caught in the crossfire if other signals are weak or negative. Let's explore why this happens and what steps you can take to improve your inbox placement.
Gmail's spam filters are incredibly advanced, using machine learning to analyze countless data points for every incoming email. While a failing authentication check is a strong indicator of spam, a passing one doesn't automatically grant you an inbox pass. Google explicitly states that even if a message passes authentication, it can still be sent to spam if it's identified as potentially suspicious. This multi-layered approach means that even with perfect authentication, other elements of your sending practices might be triggering red flags.
The core reason often boils down to sender reputation. This is a score assigned to your sending domain and IP address, built up over time based on various behavioral and technical signals. A low sender reputation can cause emails to go to spam, regardless of authentication. For example, if your Google Postmaster Tools (GPT) dashboard shows green across the board but your messages are still hitting spam, digging deeper into the old-school GPT data might reveal a different story about your domain's reputation, as I've seen in many cases.
If your emails started going to spam from day one, even with proper authentication and low sending volume, it suggests your domain or IP might have inherited a poor reputation, or you launched without adequately warming up the new sending infrastructure. A well-established, previously unused domain might have a better starting point than a brand-new one. Understanding how email domain reputation works is essential for long-term deliverability.
Sender reputation: the crucial non-authentication factor
Authentication passing
Your SPF, DKIM, and DMARC records are correctly configured and pass verification checks by the receiving server. This verifies that your email is legitimate and not a spoofing attempt. It's the technical baseline for trusted sending.
SPF: Sender Policy Framework validates the sending IP.
DKIM: DomainKeys Identified Mail adds a digital signature to verify content integrity.
DMARC: Domain-based Message Authentication, Reporting, and Conformance aligns SPF and DKIM, and defines policy for failures.
Your sender reputation is arguably the most critical factor after authentication. Mailbox providers assess your domain and IP's history across multiple signals to determine if your email is legitimate or spam. This reputation is built on how recipients interact with your emails.
Low engagement rates are a strong negative signal. If thousands of emails are sent but very few are opened or clicked, Gmail’s filters learn that your emails aren't valuable to recipients, flagging them as spam. Even if users aren't explicitly marking your emails as spam, a low open rate (e.g., 5% or less) on its own can indicate that messages aren't reaching the inbox. This also explains why your sender reputation can lead to emails getting spam-folded, a common issue.
User complaints, even if low, have a disproportionately large impact. A single spam complaint from a user is a powerful negative signal. If your Google Postmaster Tools (GPT) shows zero complaints, it might actually be a sign that your emails are going straight to spam, preventing users from even seeing them to report. This is why it's so important to dig into the old-school GPT data for your domain reputation to get the full picture.
Content, list hygiene, and user engagement
The problem
Even with perfect SPF, DKIM, and DMARC passing, your marketing emails land in Gmail spam.
Misleading GPT reports: Dashboard shows good reputation, but deeper analysis reveals a bad one.
Low engagement: Open rates are very low, especially for Gmail recipients, despite efforts to capture consent.
New sending domain: The domain is either new or has a dormant history, effectively starting with no reputation.
Root causes
Gmail's filtering algorithms prioritize user engagement and behavior over technical authentication alone. If users don't interact positively with your emails, they'll likely go to spam.
Sender reputation (IP/domain): Negative signals from past sending behavior, or lack of established trust.
User dissatisfaction: Recipients aren't finding your emails valuable, even if they didn't explicitly complain. For example, not recognizing the sender domain or expecting different content.
List quality: Potential for inactive users, or a mismatch between expressed interest and content.
Content quality and relevance play a significant part. Gmail inspects your email's content, including subject lines, body text, links, and even image-to-text ratios. Certain keywords or formatting that resemble spam can trigger filters. The use of URL shorteners, even from reputable sources like YouTube, can sometimes be flagged if the ESP's link-wrapping domain has a poor reputation, or if the shortener itself is associated with suspicious activity. While a native YouTube shortener is generally fine, it's worth checking the actual click-tracking domain used by your ESP.
Your subscriber acquisition methods and list hygiene are also critical. While you're obtaining opt-in consent, consider how strongly users expect your messages. If your sign-up process allows users to opt-in but doesn't clearly set expectations for the type and frequency of emails, they might quickly lose interest or perceive your messages as uninvited, even if they technically agreed to receive them. This can lead to silent disengagement, where users simply ignore or delete your emails, which still negatively impacts your sender reputation.
The consistency between your sending domain and the website where users signed up is also a factor. If the domain sending your marketing emails is completely different from the primary domain your users interact with, it can lead to confusion and a higher likelihood of users marking your email as spam. This lack of brand consistency can erode trust, regardless of technical authentication passes. Mailbox providers value clear sender identity for a positive user experience.
Another often overlooked aspect is the timing and cadence of your sends, particularly for onboarding series. Sending daily batches of onboarding emails, rather than immediately as a user signs up, might disconnect the email from the user's initial interaction. While 80-150 emails per day is not a high volume that typically requires extensive IP warmup for an already established domain, if the domain is effectively new to sending email, even this volume might be too much if the reputation isn't built. Consistent, timely delivery that aligns with user expectations is key.
Strategies for improving inbox placement
Improving deliverability when authentication passes requires a shift in focus from technical setup to recipient behavior and sender reputation. First, analyze your engagement data closely, breaking it down by recipient domain. If Gmail recipients have significantly lower open rates, it confirms the spam folder issue. Focus on re-engaging users who have previously opened or clicked your emails, as positive engagement is the most powerful signal to Gmail.
Submitting feedback to Google via their bulk sender feedback form, especially with detailed header information, is a proactive step. This provides direct insight into your sending practices and can help improve your reputation over time. Remember that recovering a poor domain reputation can take weeks to months, depending on the severity of the problem.
Consider the journey of your new subscribers. Ensuring the email's content and sender align with their expectations from the sign-up process is crucial. If your transactional and marketing emails come from different domains, ensure clear branding connects them. Regular monitoring of your email deliverability performance and adapting your strategy based on engagement metrics will be key to long-term success.
Views from the trenches
Best practices
Actively segment your email list based on engagement to prioritize sending to your most active subscribers.
Always align the sending domain with the primary website domain users interact with for consistency.
Continuously monitor engagement metrics, especially opens and clicks, broken down by recipient domain.
Ensure your sign-up process clearly sets expectations for email content and frequency.
Common pitfalls
Relying solely on passing authentication checks without considering sender reputation and engagement.
Using a sending domain that is unfamiliar or inconsistent with the brand users signed up for.
Ignoring low open rates, which are strong indicators of emails landing in the spam folder.
Failing to warm up a new or dormant sending domain, even for seemingly low volumes.
Expert tips
If your domain started in the spam folder, positive engagement from current openers is your best path to recovery.
The age of your domain, even if unused, can influence its initial trust level with mailbox providers.
A YouTube shortener link is usually fine, but verify your ESP's click-tracking domain is reputable.
Manual batch sending of onboarding emails might lead to a disconnect from the initial user sign-up.
Expert view
Expert from Email Geeks says the YouTube link is almost certainly wrapped by your ESP click tracker, so it is likely not an issue.
2024-07-31 - Email Geeks
Expert view
Expert from Email Geeks says a 5% or less open rate suggests messages are probably not reaching the inbox often.
2024-07-31 - Email Geeks
Getting your emails where they belong
Achieving excellent inbox placement in Gmail extends far beyond simply passing authentication checks. While SPF, DKIM, and DMARC establish your email's authenticity, your sender reputation, content relevance, list hygiene, and user engagement are equally, if not more, influential. By focusing on these holistic factors, you can build a stronger relationship with Gmail's filters and consistently reach your subscribers' inboxes, not their spam folders.
Gmail spam.
Gmail recipients, despite efforts to capture consent.
YouTube shortener is generally fine, it's worth checking the actual click-tracking domain used by your ESP.
