What could cause email deliverability or domain reputation to suddenly drop?
Matthew Whittaker
Co-founder & CTO, Suped
Published 18 May 2025
Updated 19 Aug 2025
7 min read
Experiencing a sudden drop in email deliverability or domain reputation can be a bewildering and frustrating issue for any sender. It often feels like you've been doing everything right, yet suddenly your emails are landing in spam folders, getting rejected, or your engagement metrics plummet. This abrupt change can severely impact your communication, marketing efforts, and ultimately, your business bottom line.
When your email performance takes an unexpected nosedive, it’s a clear signal that something has shifted in how mailbox providers view your sending practices. These providers, such as Gmail and Outlook/Hotmail, constantly evaluate numerous factors to determine if your emails are legitimate or potential spam. A sudden drop means one or more of these factors has triggered a negative response.
Understanding these triggers is paramount to diagnosing the problem and implementing effective solutions. This guide will walk through the primary culprits behind sudden drops in email deliverability and domain reputation, helping you identify what might have gone wrong and how to get back on track.
Authentication failures and DNS issues
One of the most immediate and impactful causes for a sudden drop is an issue with your email authentication. SPF, DKIM, and DMARC are fundamental protocols that verify your sending legitimacy. If any of these become misconfigured, or if changes are made to your sending infrastructure without updating these records, it can lead to emails being rejected outright or routed directly to spam folders.
For example, migrating to a new email service provider (ESP) or even adding a new sub-domain for sending emails can necessitate updates to your DNS records. Failure to do so means recipient servers cannot verify that the emails are truly coming from your domain, leading to trust issues. This can quickly degrade your domain's reputation.
Incorrect DKIM signatures or an invalid SPF record that exceeds the 10-lookup limit can also cause significant deliverability problems. These are technical details that, if overlooked, can have disproportionately large negative effects on your sending. Regular audits of your authentication records are essential.
Your sender reputation, both for your domain and IP address (if dedicated), is largely a reflection of how recipients interact with your emails. A sudden drop in deliverability often correlates with a swift decline in these engagement metrics. Mailbox providers closely monitor open rates, click-through rates, and, most critically, spam complaints.
An unexpected surge in spam complaints, even from a small segment of your audience, can instantly signal to providers that your emails are unwanted. This can happen if you start sending to an old or unengaged list, or if the content of your emails changes dramatically. Similarly, a spike in bounce rates, particularly hard bounces (invalid addresses), indicates a poor list hygiene which also hurts your reputation significantly.
Spam traps are another notorious culprit. These are email addresses set up by mailbox providers and blocklist (or blacklist) operators to catch spammers. Sending to a spam trap, even unintentionally, can cause immediate and severe damage to your reputation, often resulting in your domain being blocklisted. Maintaining a clean and engaged email list is crucial for sustained deliverability.
Positive engagement indicators
High open rates: Recipients are actively opening your emails, showing interest.
Strong click-through rates: Many recipients are clicking on links within your emails.
Replies and forwards: Some users are actively engaging, indicating high value.
Low unsubscribe rate: Your audience finds your content relevant and helpful.
Negative engagement indicators
High spam complaint rate: Recipients are marking your emails as spam.
The actual content of your emails plays a significant role in deliverability. Mailbox providers use sophisticated spam filters that analyze everything from keywords and link shorteners to image-to-text ratios. A sudden inclusion of spammy keywords, excessive capitalization, or suspicious links can trigger these filters, leading to inbox placement issues or even rejections.
Beyond content, inconsistent sending patterns can also raise red flags. Mailbox providers expect a certain volume and frequency from reputable senders. A sudden surge in sending volume from a domain that usually sends moderate volumes can be perceived as a spam attack, even if your intentions are legitimate. This is why proper warm-up processes are crucial for new IPs or domains.
Mixing email types, such as sending both transactional and marketing emails from the same IP address or domain, can also confuse filtering algorithms. While not always a direct cause of a sudden drop, it can make it harder to diagnose issues as you might have mixed reputation signals. Dedicated IPs and domains for different email streams often provide better control over your reputation.
IP and domain blocklists
Being listed on an email blocklist (also known as a blacklist) is one of the quickest ways to see your deliverability plummet. These lists compile IP addresses and domains associated with sending spam. Once you're on a major blocklist, many mailbox providers will simply reject your emails or send them straight to the junk folder without a second thought. Sometimes, entire IP ranges can be blocklisted if one sender on that range has a severe spam issue, affecting innocent parties.
Common reasons for landing on a blocklist include sending to spam traps, a sudden spike in spam complaints, sending unsolicited emails, or even a compromised account sending spam without your knowledge. Regular monitoring of major blocklists is crucial to detect and address these issues promptly, as delisting can take time and effort.
Key impact of blocklisting
When your domain or IP address ends up on a major blocklist, it signals to receiving mail servers that your emails are likely unwanted or malicious. This often results in a significant increase in email rejections and spam folder placement across a wide range of mailbox providers. Even if your content and list quality are good, the blocklist entry overrides these positive signals.
For example, Google and Microsoft pay close attention to blocklist status as part of their comprehensive sender reputation assessment. Ignoring a blocklist entry will perpetuate deliverability problems and can make recovery much more difficult over time. Prompt action is always recommended to mitigate the impact and begin the delisting process.
Other contributing factors
Sometimes, a sudden drop in deliverability isn't due to a single, obvious factor, but rather a combination of subtle shifts or external influences. For example, a change in how a major mailbox provider like Gmail or Yahoo updates its filtering algorithms can impact even well-behaved senders. Additionally, a new wave of phishing attacks or spam campaigns originating from shared IP ranges could inadvertently affect your sending reputation.
Internal changes within your email sending setup, such as a different sending platform, a new email template, or even minor changes to your domain's DNS records, can sometimes trigger unexpected issues. It's crucial to systematically review any recent changes made within your own environment when facing a sudden deliverability drop.
Views from the trenches
Best practices
Monitor email authentication (SPF, DKIM, DMARC) regularly for proper configuration and alignment.
Maintain a clean and engaged email list by regularly removing inactive subscribers and hard bounces.
Segment your audience and personalize content to increase positive engagement signals.
Warm up new sending IPs or domains gradually to build a positive sending history.
Keep an eye on key email metrics like open rates, click rates, and spam complaints using postmaster tools.
Common pitfalls
Ignoring sudden increases in bounce rates or spam complaints, assuming they are minor.
Purchasing or renting email lists, which often contain spam traps and unengaged contacts.
Making significant changes to email volume or sending frequency without proper warm-up.
Neglecting email authentication, leading to spoofing opportunities and deliverability issues.
Sending irrelevant or generic content to a broad audience, decreasing engagement.
Expert tips
Always check your Google Postmaster Tools for sudden reputation changes and detailed insights.
A sudden dip often points to a specific event, like a new campaign, list upload, or configuration change.
Don't solely rely on open rates for deliverability; focus on true inbox placement and engagement.
Engage in feedback loops with major mailbox providers to receive timely spam complaint data.
Consider segmenting lists by engagement level to protect your sender reputation when sending.
Marketer view
Marketer from Email Geeks says they saw a dip in their domain reputation to 'low' since late December, with no significant changes in their mailing behavior.
2020-01-19 - Email Geeks
Marketer view
Marketer from Email Geeks noted similar drops from 'Green' to 'Yellow' for several reputable domains, without any changes to their practices or lists, starting around January 9th.
2020-01-21 - Email Geeks
Restoring your email sending health
A sudden drop in email deliverability or domain reputation can be disconcerting, but it’s rarely without a cause. By systematically investigating potential issues related to email authentication, sender reputation, content, sending practices, and blocklist (or blacklist) status, you can pinpoint the problem.
Proactive monitoring and adherence to best practices are your strongest defenses against these sudden drops. Regularly checking your metrics, auditing your authentication, and maintaining a healthy email list will help ensure your messages continue to reach the inbox, protecting your crucial communication channels and overall email success.
Google and 
Microsoft pay close attention to blocklist status as part of their comprehensive sender reputation assessment. Ignoring a blocklist entry will perpetuate deliverability problems and can make recovery much more difficult over time. Prompt action is always recommended to mitigate the impact and begin the delisting process.
