Are COVID-19 related emails causing deliverability issues?
Matthew Whittaker
Co-founder & CTO, Suped
Published 18 May 2025
Updated 15 Aug 2025
9 min read
The onset of the COVID-19 pandemic brought about unprecedented changes in global communication, and email was at the forefront. As businesses and organizations scrambled to disseminate crucial information, updates, and policy changes, many senders experienced a sudden shift in their email deliverability rates. This led to a widespread concern: were emails containing terms like 'COVID-19' or 'coronavirus' inherently being flagged as spam or blocked by mailbox providers?
It was a logical question, given the sudden influx of communications on this single topic and the concurrent rise in COVID-19 related phishing and scam attempts. The landscape became saturated, making it harder for legitimate messages to cut through the noise. People were also becoming more selective about which emails they engaged with, especially those related to the pandemic, as noted by EmailMonday.
However, the reality of email deliverability during this period was more nuanced than a simple keyword filter. While the content of emails certainly played a role, the primary drivers of deliverability issues were often rooted in fundamental sending practices that were amplified by the unique circumstances of the pandemic.
The surge in COVID-19 communications
One of the most immediate impacts of the pandemic was an unprecedented surge in email volume. Many businesses increased their sending frequency, with some reporting a jump of more than 55% in delivered emails as highlighted by Rhythm Agency. This surge was driven by the need to communicate rapidly evolving situations, from store closures and remote work policies to health guidelines and emergency relief efforts. Mailbox providers and internet service providers (ISPs) were suddenly faced with a significantly increased inbound traffic load, which put a strain on their systems. Ongage's blog reported that some email providers struggled to handle this increased volume, leading to potential delays or delivery issues.
Compounding this issue was the temptation for companies to reactivate old, dormant, or opted-out email addresses in an attempt to reach every possible contact with urgent COVID-19 updates. This practice, while seemingly well-intentioned, often backfired. Sending to unengaged or non-existent addresses can lead to increased bounces and spam complaints, severely damaging a sender's reputation. This is a common pitfall that can harm email deliverability issues regardless of the message content.
Furthermore, malicious actors quickly capitalized on the global health crisis, launching widespread phishing and scam campaigns disguised as legitimate COVID-19 information or relief efforts. These fraudulent emails often mimicked official communications from government agencies, healthcare organizations, or reputable businesses. Mailbox providers, therefore, heightened their vigilance, deploying more aggressive spam filters to protect users from these emerging threats, as highlighted by Barracuda's threat spotlight. This increased scrutiny meant that even legitimate senders had to be extra cautious to ensure their emails met stringent deliverability requirements.
The real impact on deliverability
Despite initial concerns, the mere presence of terms like 'COVID-19' or 'coronavirus' in email content or subject lines was generally not the primary cause of deliverability issues. Mailbox providers, such as Google and Microsoft (Microsoft), rely on sophisticated machine learning algorithms that assess a multitude of factors to determine if an email is legitimate or spam. These algorithms are designed to avoid broad-brush blocking based on single words, especially for topics with high legitimate communication volume. Blocking every email with "COVID-19" would have been catastrophic for essential communications.
The actual culprits behind declining deliverability were often poor sending practices exacerbated by the crisis. For example, sending emails to outdated or unengaged lists dramatically increased bounce rates and spam complaints. These are strong signals to ISPs that a sender may not be adhering to best practices, leading to a damaged sender reputation. Mailbox providers typically check for valid email addresses and sender reputation signals long before analyzing the specific content of the message, with Yahoo being a notable exception that processes content earlier.
A damaged sender reputation means your emails are more likely to land in the spam folder or be rejected outright, regardless of whether they contain crisis-related terms. This is why some senders observed deliverability issues with their COVID-19 emails: it wasn't the words themselves, but rather the underlying issues with their list quality or sending behavior that surfaced more prominently during a period of increased scrutiny and volume. Many experienced senders already knew that specific spam words don't affect deliverability on their own.
Mailbox providers understand that essential communications, especially during a public health crisis, need to reach inboxes. Their filtering systems prioritize legitimate mail while aggressively targeting phishing and spam. Therefore, they focus on comprehensive signals such as sending volume fluctuations, bounce rates, complaint rates, and engagement metrics rather than simple keyword matches. This nuanced approach helps minimize false positives and ensures critical information reaches its intended recipients.
Misconception: keywords are the problem
Many believed that subject lines or content containing terms like 'COVID-19' or 'coronavirus' were automatically triggering spam filters, leading to reduced inbox placement. This perception often led to unnecessary self-censorship of crucial information.
Direct keyword blocking: The idea that a single word or phrase could cause an email to be blocklisted.
Content-first filtering: Belief that email content is the first thing checked by filters, before sender reputation.
Reality: sender reputation is paramount
Deliverability is primarily driven by sender reputation, list hygiene, and adherence to email best practices. High volume, unengaged lists, and spam complaints were the real issues.
Sender reputation first: Mailbox providers assess your overall sending behavior and trustworthiness first. This includes metrics like bounce rates and spam complaint rates. For example, Yahoo is one of the few that checks content earlier.
Engagement is key: High engagement (opens, clicks) signals good content, while low engagement, unsubscribes, or spam reports negatively impact reputation.
This insight is crucial. While it might have felt like a new challenge, the deliverability problems during the pandemic were largely intensified versions of existing issues. Senders who maintained good list hygiene and sender reputation before the crisis generally fared better.
Therefore, if your emails mentioning COVID-19 experienced deliverability problems, it's highly likely that the underlying cause was not the mention of the pandemic itself, but rather an issue with your email list quality, sender reputation, or adherence to email sending best practices. The high volume and increased scrutiny merely brought these pre-existing vulnerabilities to the surface.
Best practices for crisis communication
To navigate such high-stakes communication periods effectively, adhering to fundamental email deliverability best practices becomes even more critical. Prioritizing email list hygiene is paramount. Regularly cleaning your list to remove inactive, invalid, or unengaged subscribers reduces bounces and spam trap hits, safeguarding your sender reputation.
Segmenting your audience and sending only relevant messages is also vital. During a crisis, while broad announcements might be necessary, personalized and targeted communications based on user preferences and past engagement can significantly improve open rates and reduce complaints. For example, if you are a bulk sender using Salesforce Marketing Cloud, segmenting can help prevent deliverability problems.
Furthermore, ensuring your emails are properly authenticated with SPF, DKIM, and DMARC is non-negotiable. These protocols verify that your emails are legitimate and prevent spoofing and phishing attempts, which are particularly prevalent during crises. Implementing a strong DMARC policy, like p=quarantine or p=reject, sends a clear signal of trustworthiness to mailbox providers.
Maintaining positive sender reputation
Proactive list hygiene: Regularly clean your email lists to remove bounces, unsubscribes, and inactive users.
Segmented sending: Tailor your communications to specific, engaged segments of your audience.
Strong authentication: Implement and monitor SPF, DKIM, and DMARC to verify sender identity.
Monitor deliverability metrics: Keep a close eye on your bounce rates, spam complaints, and inbox placement.
Long-term deliverability lessons
The COVID-19 pandemic served as a stark reminder that robust email deliverability isn't just about avoiding certain keywords. It's about building and maintaining a strong sender reputation through consistent adherence to best practices. This includes proper list management, engaging content, and solid technical foundations. Issues that might have been minor before, like slightly inflated bounce rates, became critical under the increased pressure and scrutiny of a global crisis.
The lessons learned from this period are enduring. They highlight the importance of proactive measures, such as continuous email list hygiene and strategic audience segmentation, to ensure your messages reach the inbox regardless of external circumstances. A strong deliverability foundation means your email program is resilient, capable of handling sudden shifts in volume or content focus without adverse effects.
Ultimately, the answer to whether COVID-19 related emails caused deliverability issues is complex. It wasn't the content alone, but rather a combination of increased volume, heightened phishing threats, and underlying poor sender practices that became exposed. By focusing on sender reputation, engagement, and proper authentication, businesses can ensure their critical communications are always delivered effectively, in times of crisis and beyond.
Example DMARC record to ensure strong authenticationDNS
Steady, predictable sending patterns for most businesses.
Significant and sudden increase due to widespread communication needs.
Spam complaints
Reflected general list health and engagement.
Increased for senders using unengaged lists or sending irrelevant content.
Engagement rates
Varied by industry and content, generally stable.
Highly variable; high for essential updates, low for irrelevant or over-communicated content.
Phishing activity
Consistent but not tied to specific global events.
Exploited COVID-19 themes, leading to heightened ISP scrutiny and blocklisting for suspicious patterns.
Views from the trenches
Best practices
Actively manage email lists to remove inactive or bouncing addresses, which helps maintain a healthy sender reputation.
Segment audiences carefully and send targeted, relevant communications to reduce spam complaints and improve engagement.
Always ensure proper email authentication (SPF, DKIM, DMARC) is in place to verify sender identity and prevent spoofing.
Monitor deliverability metrics like bounce rates and spam complaint rates closely, especially during periods of high sending volume or sensitive topics.
Common pitfalls
Reactivating old, unengaged email addresses, leading to high bounce rates and increased spam complaints.
Assuming that crisis-related keywords in content or subject lines are the direct cause of deliverability issues.
Failing to adequately authenticate emails, making them more susceptible to being flagged as phishing attempts.
Ignoring overall sender reputation metrics while focusing solely on content-based filtering theories.
Expert tips
Mailbox providers primarily filter based on sender reputation and engagement, not individual keywords, particularly for widely discussed topics.
Most providers reject emails to non-existent addresses before even processing the message content.
Spam filters use complex machine learning algorithms that consider many signals, not just single words or phrases.
ISPs are generally aware of the need for legitimate crisis communications and avoid overly broad blocking rules.
Expert view
Expert from Email Geeks says that during the deliverability call two weeks ago, they found no evidence or reports from trusted sources that customers sending COVID-related emails were being blocked.
2020-04-06 - Email Geeks
Expert view
Expert from Email Geeks says that companies reactivating email addresses from a decade ago are having significant issues, not because of COVID content, but due to sending to disengaged users who will complain.
2020-04-06 - Email Geeks
Our conclusions
In summary, while the surge in COVID-19 related communications and the corresponding increase in phishing attempts created a challenging environment for email deliverability, the content of legitimate emails was rarely the direct cause of blocking or spam filtering. Instead, issues arose from increased email volume putting strain on systems, senders reactivating old lists leading to higher bounces and complaints, and general weaknesses in sender reputation being exposed under heightened scrutiny.
The key takeaway is that foundational email deliverability principles remain paramount. Maintaining clean lists, authenticating your sending domains, and ensuring high engagement with your subscribers are the most effective strategies to ensure your emails reach the inbox, whether you're communicating during a crisis or in normal times. These practices are crucial for navigating any evolving email landscape and ensuring your messages consistently connect with your audience.
