How can I resolve email delivery errors due to tempfail and suspected spam?
Matthew Whittaker
Co-founder & CTO, Suped
Published 17 Jun 2025
Updated 17 Aug 2025
8 min read
Email delivery can be complex, and encountering errors like "tempfail" or messages flagged as "suspected spam" is a common challenge. These issues indicate that your emails are not reaching their intended recipients, which can significantly impact your communication and business operations. Understanding what these errors mean is the first step toward resolving them.
A "tempfail" (temporary failure) often signals a transient problem, meaning the recipient's server is temporarily unable to accept your email. While this suggests the server might retry delivery later, persistent tempfails can point to deeper, underlying issues. These temporary rejections are frequently a soft signal that something is amiss, often preceding more severe blocking if not addressed.
When an email is marked as "suspected spam," it means the recipient's email provider (like Google or Microsoft) has evaluated your message and believes it's unsolicited or potentially harmful. This is a critical indicator that your sender reputation is at risk. Such flags can lead to messages being quarantined, sent directly to spam folders, or even outright blocked, impacting your overall email deliverability.
Understanding the problem
These errors are often intertwined, with suspected spam being a primary driver of "tempfail" messages. When mail servers suspect spam, they might initially defer delivery (tempfail) to perform additional checks or to rate limit senders, rather than outright rejecting the message immediately. If the suspicious activity continues, or the message truly is spam, it will eventually be blocked or delivered to the junk folder. This highlights the importance of addressing the root cause, which is almost always related to your sender reputation and how your emails are perceived by recipients and email providers.
The most common reason for your mail being marked as spam or experiencing tempfail issues is a poor sender reputation. This reputation is built on various factors, including your sending volume, recipient engagement, complaint rates, and adherence to email best practices. High complaint rates, in particular, tell email providers that your messages are unwanted, leading to stricter filtering and more delivery problems. You can learn more about this in our article about improving sender reputation.
To effectively diagnose these errors, analyzing bounce messages or looking at Google Postmaster Tools (GPMT) data is essential. GPMT can provide insights into your spam rate, IP reputation, domain reputation, and delivery errors. Understanding these metrics can help pinpoint whether the issue is related to your content, sending volume, or recipient engagement. A high spam rate on GPMT directly indicates that recipients are marking your emails as spam.
Sometimes, temporary deferrals can also be caused by greylisting, where a server temporarily rejects email from unknown senders and asks the sending server to retry later. This is a common anti-spam technique. While legitimate senders will retry, spammers often do not. However, if your mail server isn't retrying properly or if the greylisting is persistent, it can lead to unresolvable tempfails, similar to the Gmail TempFail error.
Improving sender reputation and trust
The single most impactful action you can take to resolve "tempfail" and "suspected spam" errors is to focus on improving your recipient engagement. If your recipients are consistently marking your emails as spam, or simply not engaging with them, email providers will interpret this as a sign that your mail is unwanted. This will lead to a damaged sender reputation. Regularly cleaning your email list to remove inactive or disengaged subscribers is crucial. A smaller, highly engaged list will always outperform a large, unresponsive one in terms of deliverability.
Beyond engagement, ensuring your email authentication protocols are correctly configured is vital. SPF, DKIM, and DMARC verify that your emails are legitimately sent from your domain. Misconfigurations or missing records can cause emails to fail authentication, leading to them being flagged as spam. Our guide on SPF, DKIM, and DMARC explains these in more detail. Ensure your DNS records are correct and that all legitimate sending sources are authorized within your SPF record.
Furthermore, if you are experiencing a high rate of unsolicited mail flags, review your list acquisition methods. Are you using single opt-in? Are purchased lists part of your strategy? These practices can quickly lead to high spam complaint rates and severe deliverability issues. Always prioritize sending to contacts who have explicitly consented to receive your emails.
Optimizing content and infrastructure
The content of your emails plays a significant role in triggering spam filters. Avoid excessive use of capitalization, exclamation marks, spam trigger words (e.g., "free," "discount," "urgent"), and suspicious formatting. Ensure your HTML is clean and well-structured. Broken links or images hosted on unreputable domains can also flag your emails as suspicious. Reviewing your email content for potential spam triggers is a crucial step in resolving deliverability issues.
The links within your emails are also scrutinized by spam filters. If your links redirect through suspicious domains or lead to sites that are known for malicious activity, your emails are likely to be flagged. This includes click-tracking domains used by your email service provider. Ideally, these should be custom domains aligned with your sending domain to maintain trust. You can find more common causes of email delivery failure here.
Your email sending infrastructure, whether it's a shared IP address or a dedicated one, also impacts deliverability. On shared IP addresses, other senders' poor practices can negatively affect your reputation. If you are on a shared pool, ensure your provider actively manages reputation and removes abusive senders. For high-volume senders, dedicated IPs offer more control but require proper IP warming and consistent monitoring.
Monitoring and diagnostic tools
Regularly monitoring your email performance is key to catching and resolving issues early. Google Postmaster Tools is an invaluable, free resource for monitoring your domain and IP reputation with Gmail, including spam rates, delivery errors, and authentication status. Pay close attention to the spam rate dashboard, as a rising percentage indicates a serious problem that needs immediate attention. Our guide to Google Postmaster Tools V2 can help you navigate its features.
Beyond GPMT, review your email service provider's delivery logs. These logs contain specific SMTP response codes and messages from recipient servers that can provide detailed insights into why your emails are failing. For example, a 421 code often indicates a temporary rejection due to rate limiting or spam suspicion. This level of detail is critical for targeted troubleshooting.
Finally, utilize blocklist (or blacklist) monitoring to ensure your IP addresses or domains haven't been listed. Being on a blocklist can severely impact your deliverability. If you find yourself on one, investigate the cause (often spam complaints or sending to spam traps) and follow the specific delisting instructions for that blocklist. Our blocklist checker can help you identify if you're listed. A comprehensive guide on email blocklists is available.
Sustaining healthy email deliverability
Resolving email delivery errors requires a holistic approach, addressing both technical configurations and content strategies. It's about building and maintaining trust with email providers and, most importantly, with your recipients. Consistent monitoring and proactive adjustments based on performance data are crucial for long-term email deliverability success. The journey to a healthy sending reputation is continuous, but the payoff in terms of inbox placement and engagement is well worth the effort.
By focusing on consent-based list growth, active list hygiene, robust authentication, and high-quality, engaging content, you can significantly reduce tempfail and suspected spam issues. Remember, your email marketing efforts will only be effective if your messages consistently reach the inbox.
Views from the trenches
Best practices
Maintain a clean and engaged email list by regularly removing inactive subscribers to improve sender reputation.
Implement strong email authentication (SPF, DKIM, DMARC) to verify your domain and prevent spoofing.
Monitor your sender reputation using tools like Google Postmaster Tools for early detection of issues.
Segment your audience and tailor content to ensure relevance and increase engagement.
Common pitfalls
Sending to unengaged or old contacts, which increases spam complaints and bounces.
Ignoring low open rates and high spam complaint metrics, indicating recipient disinterest.
Failing to implement or correctly configure email authentication protocols like DMARC.
Using purchased or scraped email lists, which often contain spam traps and invalid addresses.
Expert tips
If your emails are experiencing tempfails due to suspected spam, review your acquisition methods. Ensure explicit consent for all subscribers.
Analyze your email content for spam trigger words, unusual formatting, or suspicious links that might flag filters.
Don't rely solely on internal tests; true campaign performance reflects your actual sending infrastructure.
A low sender reputation can impact your entire business, not just email deliverability. Address underlying issues affecting customer satisfaction.
Expert view
Expert from Email Geeks says: You need to stop mailing people who do not want to hear from you.
October 4, 2024 - Email Geeks
Expert view
Expert from Email Geeks says: The problem isn't bounces, and it isn't unsubs, the core issue is that the recipients simply do not want your mail.
Google or 
Microsoft) has evaluated your message and believes it's unsolicited or potentially harmful. This is a critical indicator that your sender reputation is at risk. Such flags can lead to messages being quarantined, sent directly to spam folders, or even outright blocked, impacting your overall email deliverability.
