Why does Gmail mark emails from unindexed domains as dangerous?
Matthew Whittaker
Co-founder & CTO, Suped
Published 17 Jul 2025
Updated 19 Aug 2025
7 min read
You have just launched a new website or a new email sending domain, and you are starting to send out transactional or marketing emails. Suddenly, you notice something alarming: emails sent from your new domain are being flagged by Gmail with a "This message seems dangerous" warning, or even worse, sent directly to the spam folder. This is a common and frustrating experience for many new senders, especially when your emails are legitimate and adhere to all technical standards like DKIM.
The immediate thought might be that your domain is unindexed by Google's search engine, leading to this warning. While a lack of web presence can contribute, the primary reason Gmail marks emails from new or less established domains as dangerous goes deeper than simple search indexing. It is more about a lack of established trust and reputation within Gmail's comprehensive email filtering systems.
I will explain why this happens, the factors Gmail considers, and what you can do to build a strong sending reputation and ensure your emails reach the inbox safely.
The signal of unindexed domains
When we talk about an "unindexed domain" in the context of email deliverability, it refers less to its presence in search results and more to its standing within Gmail's internal reputation systems. Gmail relies heavily on historical data and established trust signals to determine a domain's legitimacy. A brand-new domain, even one with a fully functioning website, simply lacks this history.
This lack of historical data immediately raises a red flag. Many spammers and phishers register new domains frequently, use them for a short period to send malicious emails, and then discard them. Because of this common abuse pattern, Gmail's algorithms are inherently suspicious of domains without a proven track record of sending legitimate mail.
Even if your domain meets all technical email standards like SPF, DKIM, and DMARC, its youth and lack of established sender reputation mean it is operating in a grey area. Gmail's systems err on the side of caution to protect its users, leading to the "dangerous" label.
Unindexed by search engines
This means your website is not yet fully crawled and cataloged by search engines like Google Search. It primarily impacts your visibility in web search results.
Gmail's security philosophy
Gmail's overarching mission is to provide a secure and clean inbox experience for its users. This involves a multi-layered security approach designed to detect and block spam, phishing attempts, malware, and other malicious content before it reaches the user.
The "This message seems dangerous" warning is a critical component of this defense system. It is designed to alert users to potential threats that might have bypassed initial spam filters. These alerts can appear for various reasons, including suspicious links or unusual sender behavior. You can learn more about this specific warning in our guide on what the Gmail alert means.
This proactive filtering, while beneficial for user safety, can inadvertently affect legitimate new senders. Gmail's systems are constantly evaluating sender reputation, and without a positive history, a domain is treated with increased scrutiny. This often leads to new domains being caught in the net designed to protect against malicious actors.
Challenges for new domains
Lack of historical data means no established trust with inbox providers.
Higher scrutiny by spam filters, leading to potential delivery issues.
Risk of being flagged as suspicious or dangerous without proper warm-up.
Gradually warm up your new sending domain to build reputation.
Maintain clean recipient lists and monitor engagement metrics.
Key factors influencing the 'dangerous' label
While a new domain's lack of history is a significant factor, several specific elements contribute to Gmail marking emails as dangerous:
1. Email authentication (SPF, DKIM, DMARC): Even if configured correctly, new domains need time for these records to be fully recognized and trusted by all mailbox providers. Without these in place, your emails are much more likely to be flagged. Learn more about DMARC, SPF, and DKIM.
2. Content and links within the email: Gmail's filters scan email content for suspicious patterns. This includes generic or overly promotional language, unusual formatting, and especially links to unverified or newly registered domains. Using too many redirects or suspicious-looking URLs (even if legitimate) can trigger alerts. Our article on phishing warnings in Gmail delves deeper into this.
3. Sending volume and patterns: Sending a large volume of emails from a brand-new domain is a major red flag. This pattern is commonly associated with spam campaigns. Gmail expects senders to gradually increase their volume, a process known as domain warming.
4. User engagement: A lack of positive engagement (opens, clicks, replies) combined with negative signals (marking as spam, deletions without opening) can quickly tank a new domain's reputation. Gmail's spam filters learn from user actions, making positive engagement crucial.
Remediation and building trust
Overcoming the "dangerous" label requires a strategic approach focused on building trust and demonstrating legitimate sending behavior.
First, implement a thorough domain warm-up plan. This means starting with very low sending volumes to your most engaged subscribers and gradually increasing the volume over several weeks. This consistent, low-volume sending helps Gmail establish a positive reputation for your domain over time. I suggest starting with 50-100 emails per day and doubling the volume every few days, depending on engagement.
Next, ensure your email authentication is impeccable. This includes correctly setting up SPF, DKIM, and DMARC records for your sending domain. DMARC, in particular, helps protect your domain from spoofing and phishing, signalling to Gmail that you are a legitimate sender. An example of a simple DMARC record is shown below. You should also regularly monitor your domain reputation using Google Postmaster Tools. This tool provides invaluable insights into your email performance and helps identify issues before they escalate.
Finally, focus on maintaining clean mailing lists and sending engaging content. Regularly prune inactive subscribers and avoid sending to purchased or old lists, as these can contain spam traps. Ensure your email content is relevant, personalized, and provides clear value to your recipients. This will encourage positive engagement, which is a strong signal of legitimate sending to Gmail. By following these steps, you can help build your domain's reputation and move past the initial "dangerous" flags.
Factor
Impact on deliverability
Age and history
New domains are inherently suspicious due to lack of established trust.
Email authentication
Proper SPF, DKIM, and DMARC build credibility and prevent spoofing.
Sending volume
Sudden high volumes from new domains are flagged as potential spam.
Content quality
Suspicious links, generic text, or poor formatting can trigger warnings.
User engagement
Positive interactions (opens, clicks) improve reputation, negative ones harm it.
Views from the trenches
Best practices
Start with very small email volumes and gradually increase over several weeks to warm up your domain.
Ensure all email authentication records like SPF, DKIM, and DMARC are correctly implemented and published.
Monitor your domain's reputation using Google Postmaster Tools for any warnings or issues.
Send engaging and relevant content to encourage positive interactions from your recipients.
Maintain a clean mailing list by regularly removing inactive or invalid email addresses.
Common pitfalls
Sending large email volumes from a brand new, unwarmed domain which often triggers spam filters.
Neglecting proper email authentication, which signals a lack of legitimacy to mailbox providers.
Including suspicious or unverified links in your emails, even if the links are technically harmless.
Having high bounce rates or spam complaint rates due to poor list hygiene.
Assuming that a domain being indexed by search engines automatically means good email reputation.
Expert tips
Implement DMARC with a reporting policy (p=none) from day one to gain visibility into your email ecosystem.
Focus on acquiring subscribers through double opt-in to ensure high quality and engagement.
Regularly check common blocklists (or blacklists) to ensure your IP or domain is not listed.
Vary your sending patterns slightly during warm-up to mimic natural user engagement.
Segment your audience and tailor content to improve relevancy and reduce spam complaints.
Expert view
Expert from Email Geeks says that once a domain is in regular use with real pages that Google can index, the dangerous warning typically goes away. Without a real web presence, there is often little that can be done.
2019-10-22 - Email Geeks
Marketer view
Marketer from Email Geeks says that experimenting with the email content by removing certain elements might help prevent the warning from appearing.
2019-10-21 - Email Geeks
Establishing trust for new domains
For new sending domains, the "dangerous" label from Gmail is not an indictment of your business but rather a reflection of Gmail's cautious approach to security. The key to overcoming this challenge is to understand that email deliverability is a long-term game built on trust and consistent positive behavior.
By meticulously implementing email authentication, executing a proper warm-up strategy, and continuously monitoring your sending reputation, you can demonstrate to Gmail that your domain is legitimate and trustworthy. Patience and persistence are crucial, as building a strong sender reputation takes time and sustained effort. You can improve your email deliverability rates over time with dedicated effort.
