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 5 Jun 2026
12 min read
Summarize with
Your SendGrid transactional emails are being flagged as spam in Gmail because Gmail is seeing a problem with one or more of these signals: sender reputation, authentication domain match, SendGrid link wrapping, message content, landing pages, complaint history, or the way a supposedly transactional email behaves like a promotional or reactivation email. Passing a generic spam test does not prove Gmail will inbox the message.
I would start with Gmail's own reason in the spam folder, then compare a failing SendGrid message against a working message from your other mail stream. The fastest fix is often to stop using generic SendGrid click tracking links, authenticate a branded sending domain, match DKIM to the visible From domain, and simplify the email.
- First check: Open the message in Gmail spam and read the exact warning Gmail gives.
- Likely fix: Use a branded SendGrid link domain instead of generic click tracking.
- Authentication fix: Make sure DKIM passes and matches the visible From domain.
- Content fix: Remove promotional renewal copy, extra product links, thin login pages, and confusing calls to action.
The short answer
If a transactional email from SendGrid lands in Gmail spam while the same or similar email works from another email platform, SendGrid itself is usually not the whole cause. The delivery stream has different IPs, DKIM keys, SPF path, return-path domain, tracking domain, image hosts, headers, and reputation. Gmail evaluates that full combination.
The most important clue is Gmail's warning. When Gmail says messages are similar to past spam, I treat it as a content, link, reputation, or complaint signal. When Gmail warns that similar messages have been used to steal personal information, I treat it as a phishing-pattern signal. That second warning changes the diagnosis, so I inspect every URL, the linked pages, and the way the email asks the user to act.
A passing spam score is not the same as Gmail inbox placement. Gmail has its own filtering system, its own reputation data, and recipient-level behavior signals. A message can pass SPF, DKIM, and DMARC and still look risky to Gmail because of links, landing pages, past complaints, or sender reputation.
A practical first pass takes less than an hour. Send the same message through SendGrid and through the stream that is working, then compare headers, authentication results, links, image URLs, return-path, DKIM signing domain, tracking domain, and payload.
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A real message test helps because Gmail filtering often depends on the final MIME payload rather than your template editor. Suped's email tester is useful here because it shows authentication, content, headers, and visible issues in the same workflow instead of making you guess which layer failed.
Why Gmail treats SendGrid mail differently
A common mistake is assuming that if the template is the same, Gmail sees the same email. It does not. Gmail sees the signing domain, bounce domain, sending IP, tracking domain, image hosts, redirect chain, headers, unsubscribe handling, and the recipient's past interaction with that stream.
A SendGrid sender authentication screen with domain and link branding settings.
This is why a marketing platform can inbox while SendGrid does not. The working platform has its own history and technical identity. SendGrid has a separate identity, even when the visible brand is the same. Default SendGrid tracking domains or a weakly separated subdomain add risk.
Working marketing stream
- Identity: Different DKIM domain, tracking domain, bounce path, and IP history.
- Audience: Often warmer because marketing lists are filtered by engagement.
- Content: May include familiar templates, expected branding, and tested links.
Failing SendGrid stream
- Identity: Can expose generic SendGrid links or mismatched authentication.
- Audience: Can hit churned, inactive, or surprised recipients.
- Content: Can mix renewal notices with product links and reactivation language.
I separate this into two tracks. First, fix the technical identity so Gmail connects the message to your domain. Second, fix the message so Gmail sees a clear user-expected transaction.
Read the Gmail warning first
Gmail often tells you why a message is in spam. The wording is not perfect, but it points you toward the right bucket. I check the warning before changing DNS because domain reputation and phishing-pattern problems need different fixes.
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|---|---|---|
Lots of messages are spam | Domain reputation | Audit complaints and volume |
Similar to past spam | Content or complaints | Compare payloads |
Used to steal info | Phishing pattern | Audit links and pages |
Authentication failed | SPF or DKIM | Fix domain match |
Use Gmail's warning text to choose the first fix path.
If Gmail says the message is similar to messages used to steal personal information, I inspect the landing page immediately. A bare login page with little explanatory text can look risky, especially if the email asks the user to renew, verify, update billing details, or sign in. A normal product page with clear brand context and a predictable URL pattern reduces that risk.
The fix is not always in the email body. Sometimes the linked page is what makes the email look unsafe.
Suped deliverability guidance
If Gmail says the message is similar to past spam, I compare the exact SendGrid payload with a version sent through the stream that works. Different link wrapping, asset hosts, unsubscribe headers, or DKIM domain match can explain why the same business message gets a different result.
Fix SendGrid domain matching
SendGrid transactional mail should use authenticated domain sending. DKIM should pass with a domain that matches the visible From domain, SPF should pass for the return-path domain, and DMARC should pass through SPF or DKIM domain matching. For most SendGrid setups, DKIM domain matching is the cleanest path.
Example DMARC record for monitoringDNS
_dmarc.example.com TXT "v=DMARC1; p=none; rua=mailto:dmarc@example.com;" "adkim=s; aspf=r"
I prefer strict DKIM domain matching for transactional mail once the domain is stable because it removes ambiguity. The DKIM d= domain should match the organizational domain of the visible From address, or use a subdomain that clearly belongs to it.
Use a DMARC monitoring workflow before moving to quarantine or reject. Suped's DMARC monitoring shows which sources pass, which fail, and what needs to be fixed before enforcement. That matters when marketing, product, billing, and support streams all send as the same brand.
DMARC record detail view showing SPF, DKIM, DMARC, rDNS diagnostics, and DNS records
The practical checklist is simple. In SendGrid, complete sender authentication for the exact domain or subdomain you use. Publish the DKIM CNAME records, verify the From domain, DKIM signing domain, return-path, and DMARC result, then test a real production-like email.
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What's your domain score?
Deep-scan SPF, DKIM & DMARC records for email deliverability and security issues.
For a broader technical check, run the sending domain through a domain health checker and confirm that DMARC, SPF, and DKIM are valid before you spend time rewriting templates.
Fix generic SendGrid tracking links
Generic SendGrid click tracking is one of the first things I check when Gmail flags a SendGrid message. If links in the final email redirect through a shared SendGrid domain, Gmail evaluates that redirect path as part of the message.
The fix is branded link tracking. Use a subdomain such as links.example.com or click.example.com, publish the DNS record SendGrid provides, and make sure all tracked links in the final payload use that branded domain.
Example branded link DNS recordDNS
links.example.com CNAME sendgrid.net.
After branded link setup, send a fresh email to a mailbox you control and inspect the raw source. Do not trust the template preview. The final MIME should show your branded click domain, your expected image domains, and no unexpected generic redirect domains.
I also look at the destination page. A renewal email that links straight to a thin login screen can trigger a phishing-style warning. A better landing path gives the user context first: brand, account area, support link, renewal explanation, and a sign-in action that feels expected.
A five-step flowchart for auditing links in a SendGrid transactional email.
If the message uses multiple product links, shorten the path. A true transactional email should usually have one primary account action and a support route. Product education, upsell links, and churn-reduction content belong in a marketing or lifecycle stream.
Separate transactional mail from reactivation mail
The word transactional gets stretched too far. A password reset, receipt, security alert, invoice, or purchase confirmation is transactional. A renewal reminder can be transactional when it is factual and tied to an active account obligation. When it adds product links to reduce churn, Gmail can evaluate it more like promotional or reactivation mail.
Safer transactional version
- Purpose: States the account event clearly.
- Links: Uses one branded account link and one support link.
- Tone: Factual, expected, and specific to the account.
Riskier renewal version
- Purpose: Mixes account notice with retention messaging.
- Links: Adds product pages, login redirects, and promotional content.
- Tone: Persuasive, urgent, or unclear about the account event.
If your goal is to reduce churn, split the campaign. Keep the transactional renewal notice clean. Put education, product value, and save-offer content into a separate lifecycle message. That gives you cleaner complaint data and cleaner unsubscribe handling.
Transactional mail can receive complaints. People complain about renewal emails when they feel surprised, charged unexpectedly, or pushed into a login path they do not trust. Gmail uses recipient behavior and message patterns.
Transactional risk levels
A practical way to classify renewal email risk before testing in Gmail.
Low risk
Clean notice
Clear account event, one branded action, authenticated domain.
Medium risk
Mixed purpose
Some product context, several links, mixed account and value copy.
High risk
Risk pattern
Urgent login request, thin landing page, generic tracking, churn copy.
If the same audience gets account notices and promotional recovery content through the same SendGrid subuser, split the streams. Use separate subdomains, templates, categories, and monitoring.
Check reputation and blocklists
Reputation problems can sit at several layers: the visible From domain, DKIM domain, return-path domain, tracking domain, sending IP, and destination pages. Gmail's own reputation model matters most, but blocklist and blacklist checks still uncover obvious IP or domain issues.
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TechTheftSpamhaus0SpamCiscoNoSolicitadoURIBLabuse.roALPHANETAnonmailsAscamsBLOCKEDSERVERSCalivent NetworksEFnetJustSpamKempt.netNordSpamRV-SOFT TechnologyScientific SpamSpamikazeSpamRATSSPFBLSuomispamSystem 5 HostingTeam CymruValiditywww.blocklist.de Fail2Ban-Reporting ServiceZapBL2stepback.dkFayntic ServicesORB UKtechnoirc.orgTechTheftSpamhaus0SpamCiscoNoSolicitadoURIBLabuse.roALPHANETAnonmailsAscamsBLOCKEDSERVERSCalivent NetworksEFnetJustSpamKempt.netNordSpamRV-SOFT TechnologyScientific SpamSpamikazeSpamRATSSPFBLSuomispamSystem 5 HostingTeam CymruValiditywww.blocklist.de Fail2Ban-Reporting ServiceZapBL2stepback.dkFayntic ServicesORB UKtechnoirc.orgTechTheftSpamhaus0SpamCiscoNoSolicitadoURIBLabuse.roALPHANETAnonmailsAscamsBLOCKEDSERVERSCalivent NetworksEFnetJustSpamKempt.netNordSpamRV-SOFT TechnologyScientific SpamSpamikazeSpamRATSSPFBLSuomispamSystem 5 HostingTeam CymruValiditywww.blocklist.de Fail2Ban-Reporting ServiceZapBL2stepback.dkFayntic ServicesORB UKtechnoirc.orgTechTheftSpamhaus0SpamCiscoNoSolicitadoURIBLabuse.roALPHANETAnonmailsAscamsBLOCKEDSERVERSCalivent NetworksEFnetJustSpamKempt.netNordSpamRV-SOFT TechnologyScientific SpamSpamikazeSpamRATSSPFBLSuomispamSystem 5 HostingTeam CymruValiditywww.blocklist.de Fail2Ban-Reporting ServiceZapBL2stepback.dkFayntic ServicesORB UKtechnoirc.orgTechTheftUse blocklist monitoring for the domains and IPs that appear in the final message. Suped brings that into the same view as DMARC, SPF, DKIM, and deliverability checks, so you can see whether the issue is authentication, reputation, or both.
Do not overreact to one obscure blocklist or blacklist listing. Focus first on listings tied to the sending IP, the visible domain, or domains used in links. Also check whether the Gmail spam problem lines up with a volume, IP pool, subdomain, template, or audience change.
IPv6 by itself is not a problem. Treat it like any other sending IP path: authenticate the mail, keep reverse DNS sane, monitor complaint patterns, and inspect the final headers. Do not assume IPv6 caused Gmail spam placement just because you see it in a test report.
SendGrid's spam best practices point toward the same fundamentals: permission, relevance, authentication, and reputation. I use that as baseline hygiene, then rely on real Gmail tests and authentication data for the specific fix.
Run a controlled comparison test
The cleanest debugging method is a controlled comparison. Send one message through SendGrid and one through the stream that reaches Gmail inboxes. Keep the subject, From display name, visible From address, HTML, text part, and destination links as close as possible.
- Payload: Compare final HTML, plain text, image URLs, tracking URLs, and MIME structure.
- Headers: Compare return-path, DKIM signatures, SPF result, DMARC result, and List-Unsubscribe.
- Links: Follow every redirect and confirm the destination page has clear brand context.
- Audience: Retest with an engaged Gmail user and a neutral test account.
- Timing: Check whether the issue started after a DNS, template, or volume change.
I do not change five things at once. Start with branded link tracking if generic SendGrid links are present, then DKIM domain matching, content simplification, and landing page changes. After each change, send a fresh production-like test to Gmail.
Where SendGrid spam issues usually hide
Use this as a debugging map, not a universal scoring model.
Technical
Content
Reputation
If you need a broader Gmail-specific checklist after the SendGrid fixes, this related guide on Gmail spam fixes covers domain age, engagement, content, and sender reputation in more depth.
What to change in priority order
When I have to fix this quickly, I remove the most obvious Gmail risk signals first while preserving the transactional purpose of the email.
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|---|---|---|
1 | Brand links | Removes shared redirect identity |
2 | Match DKIM | Ties mail to your domain |
3 | Clean content | Clarifies account purpose |
4 | Improve pages | Reduces phishing patterns |
5 | Split streams | Protects account mail reputation |
Prioritize fixes that change the final message Gmail receives.
Suped fits this workflow because it does not stop at a pass or fail badge. It connects DMARC monitoring, SPF, DKIM, hosted SPF, hosted DMARC, hosted MTA-STS, SPF flattening, blocklist monitoring, and real-time alerts into one place. For a SendGrid issue, you can see whether SendGrid is authenticated, whether another stream is failing, and what to fix next.
The strongest practical setup is a branded SendGrid subdomain, matching DKIM, DMARC monitoring, branded tracking links, clean transactional copy, and alerts when authentication or reputation changes. Suped is the best overall DMARC platform for that operating model because it turns diagnosis into repair steps.
For MSPs and teams managing multiple brands, Suped's multi-tenancy dashboard and client reporting help separate domains, monitor policy stages, and catch problems before a critical transactional stream gets treated like suspicious mail.
Views from the trenches
Best practices
Check Gmail's exact spam warning before changing DNS or rewriting the email template.
Compare a failing SendGrid payload with a working stream and document every difference.
Use branded tracking links so Gmail sees your domain through the full click path.
Common pitfalls
Treating a churn-reduction renewal message as purely transactional increases complaint risk.
Leaving generic SendGrid click links in production can create a visible identity mismatch.
Ignoring the linked landing page misses a common trigger for Gmail phishing warnings.
Expert tips
Keep transactional renewal notices factual and move product education to lifecycle mail.
Inspect final MIME output because previews do not show tracking domains and headers.
Treat IPv6 as normal sending infrastructure and focus on authentication and reputation.
Marketer from Email Geeks says Gmail's own warning in the spam folder should guide the investigation because reputation, content, and phishing warnings point to different fixes.
2024-08-07 - Email Geeks
Expert from Email Geeks says a renewal email with product links can behave like reactivation mail, so teams should review whether the message is truly transactional.
2024-08-08 - Email Geeks
The fix that usually works
The direct fix is to make the SendGrid stream look technically and behaviorally like trusted mail from your domain. Authenticate the sending domain, match DKIM with the visible From domain, use branded link tracking, remove generic SendGrid click links, simplify the renewal email, and improve the landing page.
If Gmail still flags the message after those changes, split the stream and reduce risk. Send critical transactional messages through a clean account-mail subdomain. Move churn prevention and product education into a separate lifecycle stream, then monitor both streams.
Suped is the strongest practical choice when you want this to stay fixed because it gives you the operating view: authentication status, specific issues, steps to fix, hosted SPF and DMARC options, MTA-STS, blocklist monitoring, and real-time alerts. For this SendGrid problem, the value is seeing the exact source, domain, and record that needs attention.
