Do words like 'vaccine' or 'covid' affect email deliverability?
Michael Ko
Co-founder & CEO, Suped
Published 24 Jul 2025
Updated 16 Aug 2025
7 min read
Many email marketers have wondered whether specific words, particularly those associated with sensitive or heavily discussed topics, can negatively impact email deliverability. The common concern is that terms like 'vaccine' or 'COVID' might trigger spam filters and prevent messages from reaching the inbox. On the surface, it seems like a reasonable assumption, given how easily certain terms can be associated with spam.
However, the reality of email deliverability is far more nuanced than simple keyword blacklists (or blocklists). While it's true that some words historically carried a higher risk, modern spam filters, particularly those used by major mailbox providers, have evolved significantly. They don't simply scan for a list of forbidden words and automatically route your email to the junk folder.
Today, deliverability is predominantly driven by your sender reputation, recipient engagement, and the overall context of your email. This means that while the topic itself might be sensitive, the words 'vaccine' or 'COVID' alone are unlikely to be the sole cause of deliverability issues. The focus should be on your overall sending practices rather than individual terms.
The evolution of email filtering
The way email filters operate has undergone a dramatic transformation. In the past, spam filters relied heavily on static lists of spam trigger words. However, spammers quickly adapted, finding ways to bypass these simple checks. This led to a shift towards more sophisticated, behavior-based filtering systems.
Today, major mailbox providers like Gmail and Outlook use complex algorithms that analyze hundreds of factors. These include sender reputation, engagement metrics (opens, clicks, replies), complaint rates, bounce rates, and email authentication (SPF, DKIM, DMARC). The content itself, including specific keywords, is just one small piece of a much larger puzzle.
If an email containing terms like 'vaccine' or 'COVID' lands in the spam folder, it's typically because the sender has broader reputation issues, not because of those particular words alone. A strong, trusted sender can use these terms without issue, provided their emails are legitimate and desired by the recipients.
How modern email filters evaluate content
Sender reputation: Filters primarily assess the sender's history, not just individual words.
Engagement metrics: High opens and clicks, low complaints, signal legitimacy.
Content analysis: Filters analyze the overall email for malicious patterns, not just single terms.
The unique challenge of pandemic-era communication
The COVID-19 pandemic did, however, introduce a unique challenge for email deliverability. While major providers didn't universally block emails containing 'vaccine' or 'COVID', the sheer volume of scam and misinformation emails related to the pandemic led to some localized blocking.
Some corporate IT departments and organizations using their own on-premise email security solutions implemented very strict, blunt content filters. These filters were often keyword-based, designed to aggressively combat the influx of malicious or unsolicited emails. This blunderbuss approach, while aiming to protect users, inadvertently blocked legitimate communications, such as health updates or internal employee benefits information, if they contained those terms.
It's important to differentiate between these specific, often manual, IT-level filters and the sophisticated, dynamic systems used by large email providers. While a local IT department might implement a temporary blocklist (or blacklist) on certain words, these are not indicative of global email deliverability standards or trends.
Major mailbox providers
These providers (e.g., Gmail, Outlook) use advanced machine learning to assess sender reputation and engagement as primary factors. Keywords alone are rarely decisive.
They adapt quickly to new spam trends, relying on behavioral patterns rather than static word lists.
Corporate/on-premise filters
Some organizations, particularly during crises, implemented rigid keyword-based filters to block perceived threats, affecting legitimate emails containing terms like 'COVID'.
These are localized policies and don't reflect broader internet service provider (ISP) filtering logic.
Prioritizing sender reputation and recipient trust
At the core of email deliverability is your sender reputation. This is a complex score that mailbox providers assign to your sending domain and IP address, reflecting their trust in you as a sender. Factors like complaint rates (when recipients mark your email as spam), engagement, and bounce rates all contribute to this score.
High complaint rates are particularly damaging. When recipients frequently mark your emails as spam, it sends a strong negative signal to ISPs, severely impacting your email deliverability, regardless of the words used. Conversely, strong engagement—recipients opening, clicking, and replying—boosts your reputation.
This means that if you have a healthy sender reputation, and your audience expects and values your communications, you can use words like 'vaccine' or 'COVID' in a relevant context without issues. The content becomes risky only when it's part of a broader pattern of unsolicited or unwanted mail. For instance, an official health organization communicating about public health would not face issues using these words due to their established legitimacy.
Ultimately, focusing on building and maintaining a positive sender reputation is far more effective than trying to avoid a dynamic list of spam trigger words. Your overall email program's health and the quality of your recipient list will determine your inbox placement much more than specific word choices.
High opens, clicks, and replies signal to ISPs that your emails are valued, boosting deliverability.
Complaint rate
When users mark your email as spam, it significantly damages your reputation and sends emails to spam.
Email authentication
Properly configured SPF, DKIM, and DMARC records prove your emails are legitimate and prevent spoofing.
Best practices for sensitive content
Communicating about sensitive topics requires a strategic approach beyond just word choice. The key is to ensure your messages are highly relevant, expected, and valuable to your recipients. This starts with maintaining a clean, engaged email list and segmenting it appropriately to send targeted content.
Always prioritize clear, accurate information and avoid sensational language, clickbait subject lines, or anything that could be perceived as deceptive. Transparency builds trust, which is a significant factor in how mailbox providers assess your emails. Focus on providing real value to your audience.
Regularly monitor your blocklist (or blacklist) status and your domain's reputation using tools like Google Postmaster Tools. This proactive approach ensures that even when discussing sensitive topics, your email infrastructure is robust enough to support good deliverability.
Example: Basic DMARC record to enhance trust
Implementing strong email authentication is a fundamental step to proving your legitimacy as a sender, especially when discussing sensitive topics. A DMARC record, for instance, helps protect your domain from unauthorized use and indicates to receiving servers that your emails are authentic.
Maintain a highly engaged and clean email list, regularly removing inactive subscribers to boost deliverability.
Implement robust email authentication, including SPF, DKIM, and DMARC, to verify sender identity and build trust.
Focus on clear, concise, and value-driven content that is relevant to your audience, regardless of the topic.
Monitor your sender reputation and deliverability metrics closely to identify and address issues proactively.
Common pitfalls
Sending to unengaged or purchased lists, which leads to high bounce and complaint rates.
Over-relying on keyword avoidance instead of improving overall sending practices and sender reputation.
Ignoring email authentication protocols, making it harder for ISPs to trust your messages.
Using misleading subject lines or deceptive content that prompts recipients to mark emails as spam.
Expert tips
Focus on building strong sender relationships with mailbox providers through consistent, legitimate sending volume.
Leverage DMARC reporting to gain insights into how your emails are being authenticated and delivered.
Segment your audience precisely to ensure that sensitive content is only sent to those who expect and welcome it.
A/B test subject lines and content to see what resonates best with your audience and avoids negative signals.
Expert view
Expert from Email Geeks says that major spam filters or reputation engines do not primarily focus on specific keywords like "vaccine" or "COVID." Instead, deliverability hinges on sender identity, recipient interaction, and how effectively the sender addresses negative feedback signals.
2021-09-17 - Email Geeks
Marketer view
Marketer from Email Geeks says that during the pandemic, some corporate or on-premise IT departments implemented broad content filters, blocking terms like "COVID" due to scam emails, which unfortunately impacted legitimate communications like health benefits.
2021-09-17 - Email Geeks
A holistic view of email deliverability
The belief that words like 'vaccine' or 'COVID' inherently damage email deliverability is largely a misconception in today's email landscape. While the pandemic brought about some temporary, localized challenges due to specific organizational filters, major mailbox providers operate on a more advanced, comprehensive model.
The overwhelming factors influencing whether your email lands in the inbox are your sender reputation, the authenticity of your domain (via authentication protocols), and the quality of your recipient engagement. Focus on these foundational elements to ensure strong email deliverability.
By building trust with ISPs and your audience through consistent best practices, you can confidently communicate about any relevant topic, including sensitive ones, knowing your messages are more likely to reach their intended destination. A proactive approach to email deliverability health will always yield better results than merely avoiding certain words.
Gmail and 
Outlook use complex algorithms that analyze hundreds of factors. These include sender reputation, engagement metrics (opens, clicks, replies), complaint rates, bounce rates, and email authentication (SPF, DKIM, DMARC). The content itself, including specific keywords, is just one small piece of a much larger puzzle.
