Why is Zoho Mail rejecting emails with 'Signature date is -1 seconds in the future' errors?
Matthew Whittaker
Co-founder & CTO, Suped
Published 19 Nov 2025
Updated 19 Nov 2025
8 min read
Encountering email rejections with the error message 'X-ZohoMail-DKIMfail (Signature date is -1 seconds in the future.)' can be a frustrating experience. This issue indicates that Zoho Mail is receiving your emails, but something in the DKIM signature's timestamp is causing a validation failure. When DKIM fails, it often leads to a DMARC failure, especially if your emails rely heavily on DKIM for authentication.
The core of this problem typically lies in a slight time desynchronization between your sending mail transfer agent (MTA) and the receiving Zoho Mail servers. While a one-second difference might seem negligible, it can be critical for cryptographic processes like DKIM, which depend on precise timestamps to ensure the integrity of the email. This article will delve into why this happens and what steps you can take to resolve it.
Understanding and rectifying this specific error is crucial for maintaining your email deliverability, especially if a significant portion of your recipients use Zoho Mail. A persistent DMARC failure can lead to your legitimate emails being quarantined or rejected outright, severely impacting communication and business operations.
Understanding the 'Signature date is -1 seconds in the future' error
The error message 'Signature date is -1 seconds in the future' directly points to a mismatch in the timestamp included in the DKIM signature. DKIM (DomainKeys Identified Mail) uses cryptographic signatures to verify the sender of an email and ensure that the email has not been tampered with in transit. Part of this signature includes a timestamp (the t= tag) that indicates when the email was signed. Receiving mail servers check this timestamp to ensure the signature is still valid and not expired, or, in this case, from the future.
When your MTA logs show an email sent at, for instance, 12:55:11 but Zoho Mail records receiving it at 12:55:10, it means their server's clock is effectively one second behind yours. From their perspective, your DKIM signature was created one second in the future, rendering it invalid. This seemingly minor discrepancy can have significant consequences for your email's journey to the inbox, especially if your DMARC policy is set to p=quarantine or p=reject. To learn more about common DKIM failures, consider reading our article on why DKIM shows a permerror (bad sig) on Yahoo Mail.
The problem is exacerbated if your customers are sending with an unaligned Mail From domain, relying solely on DKIM for authentication. In such scenarios, if DKIM fails, the email has no other mechanism to pass DMARC, leading to delivery issues. This highlights the importance of comprehensive email authentication and DMARC monitoring.
The role of time synchronization in email authentication
Accurate time synchronization is fundamental for secure and reliable email communication. Mail servers around the world rely on Network Time Protocol (NTP) to keep their clocks synchronized with atomic time sources. Even a slight drift, as seen with Zoho Mail having a clock one second behind, can disrupt processes that depend on precise timing, such as DKIM validation.
Time synchronization failures can manifest in various ways, not just with DKIM. They can impact TLS certificate validity checks, session timeouts, and even how logs are correlated across different systems. For email, this often means legitimate messages are unnecessarily rejected or marked as suspicious due to timing discrepancies during authentication. Our article on decoding DKIM temperror offers further insights into temporary DKIM failures.
While most major email providers have robust NTP setups to prevent such issues, some smaller or custom-configured systems might occasionally suffer from time drift. This makes Zoho Mail's strict enforcement of signature timestamps particularly challenging when inconsistencies arise. It's a reminder that even subtle infrastructure differences can lead to deliverability headaches.
Zoho Mail's strict DKIM validation
Zoho Mail's validation process appears to be particularly sensitive to the DKIM signature timestamp. While RFC 6376, which defines DKIM, recommends the inclusion of the t= tag, it doesn't explicitly mandate such strict future-dating checks for minimal time differences. This stricter approach by Zoho Mail sets it apart from many other providers who might tolerate a one-second discrepancy.
Most email providers typically account for minor time differences and network latency, validating DKIM signatures even with a few seconds of drift. This pragmatic approach ensures high deliverability while maintaining security standards. For example, Gmail often accepts emails even with slight discrepancies.
Flexible validation: Generally lenient towards minor time synchronization issues.
Higher deliverability: Fewer rejections due to clock drift, improving inbox placement.
Zoho Mail's policy, however, enforces a stricter interpretation. Even a one-second future timestamp can trigger a DKIM failure, leading to DMARC rejection or quarantine. This stringent approach means that senders need to ensure their systems are perfectly synchronized to avoid issues, as detailed by Zoho Mail's practices in email security.
Strict validation: Rejects signatures dated even marginally in the future.
Increased rejections: Higher chance of legitimate emails failing DKIM and DMARC with Zoho Mail.
The challenge intensifies when attempting to resolve this directly with Zoho Mail support, as reported by many users. This often leaves senders seeking workarounds or needing to re-evaluate their entire email authentication setup. It's also worth investigating if your email signature itself is causing delivery issues.
Mitigating the issue and DMARC implications
When facing this 'Signature date is -1 seconds in the future' error, your first step should be to verify the time synchronization of your sending infrastructure. Ensure that all your MTAs and email signing software are accurately synchronized using a reliable NTP server. Even a minor adjustment can often resolve this specific issue. You can compare the DKIM t= timestamp in the email header with your server logs.
Example MTA Log and Zoho Receipt
My MTA-logs: "11/12/2025 12:55:11 Sent 3360000012aff79 - - <test10@xxxxxxxx.xxx> xxxxx@xxxxxx.xx 295 33600000035b130 250+Message+received{CRLF} - 10.231.0.77 - <http://mx.zoho.eu>
Zoho's logs: 12 Nov 2025 12:55:10 +0100.
If adjusting time synchronization doesn't immediately fix the problem, or if you're unable to modify your signing software, you might be in a difficult position, especially if other mail providers accept your emails without issue. Modifying your DKIM signing process just for one specific provider can be disruptive and potentially introduce new issues. For a comprehensive understanding of email authentication, read our simple guide to DMARC, SPF, and DKIM.
This situation underscores the critical role of DMARC monitoring. By closely tracking your DMARC reports, you can identify specific issues with email authentication, such as DKIM failures, from different receivers, including Zoho Mail. Suped offers robust DMARC monitoring with AI-powered recommendations, real-time alerts, and a unified platform for DMARC, SPF, and DKIM, helping you quickly pinpoint and resolve deliverability problems. We also offer SPF flattening to address common SPF issues. Understanding and troubleshooting DMARC reports from Google and Yahoo is also key for overall email health.
Regularly checking your blocklist (or blacklist) status is also a good practice, as being listed can also cause rejections, even if authentication passes. A proactive approach to email deliverability, combining proper time synchronization with comprehensive monitoring, is your best defense against such elusive errors.
Views from the trenches
Best practices
Ensure all mail servers use Network Time Protocol (NTP) for accurate clock synchronization.
Regularly monitor DMARC reports to detect DKIM authentication failures promptly.
Maintain aligned SPF and DKIM records to prevent DMARC failures when one authentication method encounters issues.
Keep email signing software updated to benefit from the latest security and timing adjustments.
Common pitfalls
Ignoring small time discrepancies, as even one second can cause DKIM validation failures.
Not having a fallback authentication mechanism (like aligned SPF) when DKIM fails.
Relying solely on one email provider's support for critical deliverability issues without parallel investigation.
Overlooking the `t=` timestamp in DKIM headers during initial troubleshooting of rejections.
Expert tips
Verify your server's NTP configuration and ensure it's syncing with reliable public time servers. This foundational step resolves many timestamp-related authentication issues.
Utilize a DMARC monitoring tool like Suped to gain visibility into specific rejection reasons across all recipients. This allows for targeted troubleshooting rather than broad changes.
Test your DKIM signatures with various validation tools to catch subtle errors that might only appear with strict receivers. This can help isolate configuration problems.
When encountering unique rejections from a specific provider, consult community forums or mailing lists dedicated to mail operations. Collective experience often uncovers nuances not found in official documentation.
Marketer view
Marketer from Email Geeks says they have issues with Zoho rejecting mail due to a signature date being one second in the future, which then causes DMARC to fail for customers relying on DKIM.
2025-11-12 - Email Geeks
Marketer view
Marketer from Email Geeks says that the 't=' tag in the DKIM-Signature header is recommended, not required, and suggested experimenting with removing it to see if it helps with Zoho.
2025-11-12 - Email Geeks
The importance of precise timing for email deliverability
The 'Signature date is -1 seconds in the future' error from Zoho Mail, while specific, illustrates a broader point about the delicate nature of email deliverability. Even minor inconsistencies, such as a one-second clock drift, can trigger a cascade of authentication failures, leading to DMARC rejections and impacting your ability to reach recipients. This issue highlights the importance of precise system configuration and vigilant monitoring.
To ensure your emails are consistently delivered, especially to providers with strict validation rules like Zoho Mail, it's essential to maintain accurate time synchronization across your email infrastructure. Beyond that, a robust DMARC monitoring solution is indispensable. Tools like Suped provide the necessary visibility and actionable insights to quickly detect and resolve such complex deliverability challenges, safeguarding your email reputation and ensuring your messages land in the inbox.
By proactively addressing these technical nuances and leveraging specialized platforms, you can navigate the intricacies of email authentication and maintain optimal deliverability for all your communications. For more help with troubleshooting, explore our guides on how to fix common DMARC issues in Microsoft 365 and Google Workspace, and diagnosing DKIM temporary error rates with Microsoft.
Zoho Mail is receiving your emails, but something in the DKIM signature's timestamp is causing a validation failure. When DKIM fails, it often leads to a DMARC failure, especially if your emails rely heavily on DKIM for authentication.
