Why are my transactional emails from Sendgrid being flagged as spam in Gmail, and how can I fix it?
Matthew Whittaker
Co-founder & CTO, Suped
Published 10 Jul 2025
Updated 17 Aug 2025
8 min read
It can be incredibly frustrating when your transactional emails, especially those sent via SendGrid, inexplicably end up in the spam folder for Gmail recipients. You've checked your basic setup, and everything seems fine, yet crucial communications like password resets, order confirmations, or renewal notices are being misdirected. This isn't just an annoyance; it directly impacts user experience and trust.
Unlike marketing emails, transactional emails are expected, immediate, and often critical to a user’s interaction with your service. When they land in spam, it signals a deeper problem that goes beyond simple content issues or a low open rate. It often points to a breakdown in trust between your sending domain and the recipient's mailbox provider.
I’ve seen this scenario play out many times, and the solutions often require a multi-faceted approach. It's rarely a single silver bullet, but rather a combination of technical configurations, content adjustments, and ongoing reputation management. Let's delve into why this happens and what you can do to ensure your essential emails reach the inbox.
Understanding Gmail's filtering mechanisms
Gmail’s spam filtering is sophisticated, relying on complex algorithms that analyze thousands of signals for every incoming email. It's not just about simple keywords or a few reports; it's a holistic assessment of your sending practices and reputation. When your emails are flagged, Gmail attempts to protect its users from unwanted or malicious content. Sometimes, legitimate emails can get caught in this net.
There are generally two common reasons Gmail provides when an email is placed in the spam folder, particularly for transactional messages that have previously worked. One indicates a broader poor domain reputation, suggesting that a significant number of messages from your domain are being reported as spam. The other points to the content of the message itself being similar to past spam, or that your campaign is receiving excessive “This is Spam” votes from recipients. Sometimes, you might even see a phishing warning, which is a more severe flag.
Gmail's spam notifications
When an email is flagged as spam, Gmail often provides a reason at the top of the message in the spam folder. Understanding these messages is key to diagnosing the problem:
Poor domain reputation: The message states, "We've found that lots of messages from <domain> are spam." This indicates an issue with your sender reputation across a broader range of your emails.
Content or user reports: The message says, "It is similar to messages that were identified as spam in the past." This suggests your email content or format resembles known spam patterns, or recipients are frequently marking your emails as spam.
Phishing warning: A more severe warning like, "Similar messages have been used to steal users' personal information. Avoid clicking links..." This can occur if your email or its landing page mimics phishing attempts, even if unintentionally. You can find more information about how Gmail's sender guidelines work to protect their users.
Even with SendGrid's robust infrastructure, if Gmail (or any mailbox provider) starts flagging your emails, it usually points to specific factors related to your sending behavior, domain, or content. While authentication is crucial, it's often not the sole reason once initial setup is complete.
Common culprits for transactional emails being flagged
Several common issues can cause transactional emails sent through SendGrid to be flagged as spam by Gmail. It's essential to pinpoint which of these might be affecting your particular sending patterns.
One primary reason can be the content of the email. Even for transactional emails, adding promotional elements, excessive links, or using language that resembles marketing pitches can confuse Google's algorithms. For example, a renewal email that heavily promotes new product features rather than simply informing the user about their upcoming renewal might be misclassified.
Another often overlooked aspect is the quality of your links and landing pages. If links within your emails direct to sparse landing pages, login boxes with minimal text, or domains with a poor reputation, Gmail might flag them as suspicious or phishing attempts. This is particularly true if SendGrid is using a generic click-tracking domain (like `sendgrid.net`) instead of a custom, branded one. This can negatively impact your sender reputation, making your emails more susceptible to being blacklisted or blocklisted. You can read more about avoiding spam blocking in this SendGrid guide.
Content and link issues
The content and links within your transactional emails are crucial, especially for Gmail's advanced filters. Here's a breakdown of common problems:
Promotional content: Mixing marketing language or product promotions into transactional emails can lead to misclassification. Transactional emails should be strictly informative and directly related to a user's action.
Suspicious text patterns: Certain phrases or formatting can trigger spam filters, especially if they mimic common phishing tactics.
Generic click tracking: If SendGrid links resolve to `sendgrid.net` instead of your branded domain, it can hurt your reputation. Configure SendGrid's link branding to use your own domain.
Authentication issues
Even if you believe your authentication is set up, small misconfigurations or changes can lead to problems:
SPF records: Ensure your SPF record correctly authorizes SendGrid to send on your behalf and doesn't exceed the 10-lookup limit.
DKIM signing: Verify your DKIM records are correctly published and that SendGrid is signing your emails. Learn about common DKIM selectors.
DMARC policy: A strict DMARC policy (p=quarantine or p=reject) without proper alignment can cause emails to be rejected or spammed. Ensure your SPF and DKIM are aligned with your From domain.
Troubleshooting and diagnostic steps
When facing deliverability challenges, especially when transactional emails are going to spam, a structured troubleshooting approach is key. It's about gathering data and systematically eliminating potential causes.
The first step is to leverage Google Postmaster Tools. This free tool from Google provides invaluable insights into your domain's reputation, spam complaints, and authentication status. If your domain reputation is low, that's a strong indicator of a widespread problem. Monitoring DMARC reports will also highlight any authentication failures.
Reviewing your email content meticulously is also crucial. Look for common spam triggers, excessive images with little text, or overly promotional language that might confuse Gmail's filters. If you’ve recently added new links or redesigned your landing pages, carefully inspect them for anything that could be perceived as phishing. Even small details, like a login form on a page with minimal surrounding context, can trigger warnings. Additionally, ensure your SendGrid account has link branding enabled, so click-tracked links use your own domain, not a generic `sendgrid.net` subdomain. This simple step can significantly improve trust signals.
Finally, monitor for blacklist (or blocklist) listings of your sending IP or domain. While SendGrid manages its shared IP reputation, a sudden drop in deliverability could indicate an issue there, or if you have a dedicated IP, it might be listed. Regularly checking major blocklists is a proactive measure.
Long-term deliverability strategies
Beyond immediate fixes, long-term deliverability success, especially for transactional emails from a service like SendGrid, requires consistent attention to your email program's health.
If you are sending both marketing and transactional emails, consider separating your sending streams using different subdomains or even different ESPs (Email Service Providers). This ensures that any issues with your marketing emails (which typically have higher complaint rates) don't impact the critical deliverability of your transactional messages. Gmail (and other mailbox providers) often treat different subdomains or sending IPs as distinct entities for reputation purposes.
Finally, consistent monitoring of your email performance is non-negotiable. Don't wait for users to report spam issues. Regularly check your SendGrid analytics, Google Postmaster Tools, and DMARC reports. Pay attention to complaint rates, bounce rates, and authentication failures. Being proactive helps you identify and mitigate problems before they escalate and severely impact your ability to reach the inbox. If you’re interested in other common deliverability issues, read our article on how to fix Gmail deliverability issues.
Views from the trenches
Best practices
Maintain strict separation between transactional and marketing email content, even within a single email.
Always use a custom, branded tracking domain for links instead of SendGrid's generic `sendgrid.net` domain.
Regularly monitor your domain and IP reputation using tools like Google Postmaster Tools.
Ensure your SPF, DKIM, and DMARC records are correctly configured and aligned for your sending domain.
Proactively check for any blocklist (or blacklist) listings that could impact your deliverability.
Common pitfalls
Including promotional links or marketing-oriented language in transactional emails.
Using generic click-tracking domains (like `sendgrid.net`) instead of a custom branded one.
Not having robust DMARC policies in place, or misconfiguring them.
Ignoring phishing warnings from Gmail, as they indicate severe trust issues.
Failing to regularly check email authentication and reputation metrics.
Expert tips
If Gmail labels an email as potential phishing, analyze the landing page linked in the email.
Ensure the landing page has sufficient text content, not just a login box, to avoid suspicion.
Segment your email streams (transactional vs. marketing) to protect transactional deliverability.
Don't assume transactional emails are immune to spam complaints; users can still mark them as spam.
If an email that previously worked starts going to spam, look for recent content or link changes.
Marketer view
Marketer from Email Geeks says that SendGrid is likely not the primary factor; instead, focus on the type of transactional email being sent, as even transactional messages can receive complaints.
2024-08-07 - Email Geeks
Marketer view
Marketer from Email Geeks says that Gmail employs its own reputation and filtering systems, meaning if only the transactional stream is blocked, the audience for that particular stream might be the problem.
2024-08-07 - Email Geeks
The path to better inbox placement
Having transactional emails from SendGrid flagged as spam by Gmail is a common yet solvable challenge. It typically boils down to a combination of factors related to your domain's reputation, email content, link quality, and proper authentication. It’s crucial to treat each of these areas with diligence, understanding that Gmail's filters are designed to protect users from both unwanted bulk mail and malicious phishing attempts.
By regularly monitoring your domain's health through tools like Google Postmaster Tools, refining your email content to be purely transactional, configuring branded links, and ensuring your authentication records (SPF, DKIM, DMARC) are impeccable, you can significantly improve your inbox placement. Remember, maintaining a strong sender reputation is an ongoing effort that pays dividends in reliable deliverability.
SendGrid, inexplicably end up in the spam folder for 
Gmail recipients. You've checked your basic setup, and everything seems fine, yet crucial communications like password resets, order confirmations, or renewal notices are being misdirected. This isn't just an annoyance; it directly impacts user experience and trust.
Gmail attempts to protect its users from unwanted or malicious content. Sometimes, legitimate emails can get caught in this net.
