Summary
Email signatures, though seemingly innocuous, can significantly impact email deliverability. When emails containing a signature are not delivered, while the same email without the signature is, it suggests that elements within the signature are triggering spam filters or recipient mail server rules. Common culprits include complex HTML, embedded images, and particularly, links to domains that may have a poor reputation or be perceived as suspicious. This issue often results in silent blocking, where no bounce message is received, making diagnosis challenging.
Key findings
- Content filtering: Email signatures containing specific content, such as numerous links or complex HTML, can be flagged by spam filters, preventing delivery.
- Reputation of linked domains: A link within the signature (e.g., website, social media, call to action) pointing to a domain with a low or questionable reputation can lead to the entire email being blocked by the recipient's server.
- HTML complexity: Overly complex or poorly structured HTML in signatures can confuse mail servers, causing them to reject the email, sometimes silently.
- Silent blocking: Emails may not be delivered without generating a bounce message, making troubleshooting difficult as the sender receives no direct feedback regarding the delivery failure.
- Internal versus external delivery: Emails with signatures might deliver successfully internally (within the sender's organization) but fail when sent to external recipients due to differing security policies and filtering rules.
Key considerations
- Isolate problematic elements: Test by removing signature components one by one (e.g., images, specific links) to identify the exact cause of the delivery issue.
- Check domain reputation: Verify the reputation of all domains linked within the signature using blocklist checkers, as a compromised domain can severely impact deliverability.
- Simplify signature design: Opt for cleaner, simpler HTML and fewer external links in your signature if deliverability becomes a consistent issue.
- Monitor mail logs: If possible, check your mail server logs for evidence of delivery attempts, rejections, or error messages that might provide clues.
- Test with different recipients: Send test emails to various public email providers (like Gmail, Outlook, Yahoo) to observe different behaviors and potential warnings. This can help diagnose why your cold emails are going to spam. Consider using a tool like MySignature for testing if your signature is showing correctly.
- Improve overall deliverability: Review your email sending practices to improve overall email deliverability, as signature issues can be symptoms of broader problems.
What email marketers say
Email marketers frequently face the challenge of ensuring their email signatures are both informative and deliverable. Many recount instances where the inclusion of specific elements, such as images, social media links, or calls to action, led to emails being blocked or landing in spam folders, despite the main message being legitimate. Their experiences often highlight a trial-and-error process to identify the problematic components that cause these delivery failures.
Key opinions
- Links are often the issue: Marketers frequently find that social media links, website links, or CTA links within a signature can be flagged, especially if the linked domains have a history of issues or if there are too many external links, potentially leading to emails being blocked.
- Images cause problems: Images, particularly if embedded incorrectly or hosted on less reputable servers, can be converted to attachments or outright block emails, affecting both rendering and deliverability. Gimmio explains this behavior.
- HTML complexity and format: The way a signature is coded in HTML, or if the email client defaults to plain text, can prevent the signature from displaying or even block the entire email.
- Testing is essential: The consensus among marketers is that systematic testing, by removing elements one by one, is the most effective way to pinpoint what's causing delivery failures. This is a key part of running an email deliverability test.
- Recipient differences: Marketers observe that emails might deliver perfectly to internal recipients or some external providers (e.g., Gmail) but fail completely with others (e.g., Microsoft 365 users), indicating varied filtering sensitivities.
Key considerations
- Minimalist approach: Consider simplifying your signature, perhaps temporarily, to identify if any specific element is causing the issue. Less is often more for deliverability.
- Validate all links: Ensure all URLs in your signature are active, reputable, and not associated with spam or blocklists. Broken or suspicious links can be a major red flag.
- Optimal image embedding: Host images on reliable servers and use standard HTML for embedding rather than attachments, where possible, to improve rendering and deliverability.
- Check email client settings: Verify that your email client is consistently set to send messages in HTML format for signatures with rich content, as plain text can strip formatting.
- Learn from warnings: Utilize email providers like Gmail for testing, as they often provide clearer warnings or bounce messages that can aid in diagnosing hidden problems.
Marketer view
Marketer from Email Geeks shares their challenge. They initially reported that emails fail to deliver when an email signature is included, but they are delivered successfully once the signature is removed. This suggests the signature itself, or elements within it, are causing the deliverability problem. Further testing revealed that the emails were not bouncing back nor were they found in the spam folder, indicating a silent blocking by the recipient's mail server. This kind of invisible filtering makes troubleshooting particularly difficult for senders, as they receive no direct feedback.
Marketer view
Marketer from Email Geeks suggests a diagnostic approach. They questioned whether the emails were being delivered with the signature but without the main content, or if the entire email was being blocked. This highlights the importance of understanding the exact failure mode. They also recommended testing delivery to various email services. This method helps to identify if the issue is specific to certain recipient domains or mail providers, which can point towards particular filtering rules or reputation issues affecting those specific routes.
What the experts say
Email deliverability experts pinpoint several sophisticated factors behind email signature-related delivery failures. They emphasize that while a signature is part of the email's content, its elements can be individually scrutinized by highly sensitive spam filters and blocklists. Issues often stem from the reputation of linked domains, the complexity of HTML, and the aggressive filtering policies of certain mail service providers, leading to emails being silently dropped without notification to the sender.
Key opinions
- Domain reputation for links: Experts highlight that the reputation of any domain linked within a signature, whether a website, social media profile, or CTA, is a critical factor. A poor reputation can lead to the entire email being blocked or blacklisted, as explained in our guide on how email blacklists actually work.
- Content scanning depth: Mail servers perform deep content analysis, and elements like poorly optimized images, unusual file types for attachments (even embedded ones), or suspicious HTML tags within a signature can trigger red flags, even if the primary content is benign.
- Microsoft 365 sensitivity: Microsoft 365 (Outlook, Hotmail) is frequently cited by experts as having particularly stringent filtering. Emails that might pass through other providers can be blocked by Microsoft if their signatures contain elements deemed risky.
- Importance of authentication: While signatures themselves don't directly cause SPF, DKIM, or DMARC failures, overly complex or altered content can sometimes interfere with how these authentication protocols are interpreted by recipient servers, especially if signature content is added via third-party tools, as seen in SPF or DKIM failures and email delivery.
- Silent failures: Experts confirm that silent dropping is a common scenario, especially with content-based blocking. This lack of bounce messages necessitates proactive monitoring and testing from the sender's side to identify issues.
Key considerations
- Pre-check all linked domains: Before incorporating links into a signature, verify their current blocklist status and overall reputation to prevent deliverability problems.
- Simplify HTML and avoid complex scripts: Ensure signatures use clean, basic HTML. Avoid JavaScript or overly complex CSS that could be misconstrued as malicious by filters.
- Optimize images: Use properly sized and formatted images, ideally hosted externally and referenced via absolute URLs, to prevent them from being treated as suspicious attachments. WiseStamp outlines common Gmail signature issues, many of which relate to image handling.
- Monitor sender reputation: Understand how your overall sending domain and IP reputation might be impacted by recurring signature-related blocks and use relevant tools for insight.
- Review email headers: Analyzing email headers of successfully delivered messages can sometimes provide clues about how signatures are processed and whether they're adding to a 'spam score'.
Expert view
Expert from Email Geeks clarifies that email signatures, especially those with numerous social media links or tracking pixels, can increase an email's "spam score." Mail servers analyze the total content of an email, and an overly complex signature can contribute negatively. They explain that too many external links, even to legitimate sites, might be interpreted as an attempt to phish or distribute malware, leading to the email being blocked or routed to the spam folder. This is particularly true if the links are not consistently authenticated.
Expert view
Expert from Email Geeks states that the quality of the HTML in an email signature is paramount. Poorly coded or overly elaborate HTML structures can confuse email clients and spam filters, leading to display issues or outright blocking. They advise using clean, validated HTML for signatures to ensure maximum compatibility and deliverability across diverse email environments. Avoiding inline CSS that is overly complex or JavaScript that could be misinterpreted as malicious code is also critical.
What the documentation says
Official documentation from email clients and signature management platforms often provides specific guidelines on how to create and implement email signatures effectively. These resources typically emphasize adherence to standard HTML practices, proper image embedding, and understanding the rendering behavior across different email environments. Ignoring these documented best practices can lead to display issues or, more critically, email delivery failures that are hard to diagnose.
Key findings
- HTML format requirement: Most documentation stresses that rich signatures with images, links, or specific styling require the email to be sent in HTML format; plain text mode will not render them correctly and can lead to images appearing as attachments.
- Content placement: Some email clients or signature injection tools (e.g., Microsoft Outlook app on mobile, Xink) may have specific rules about where content can be placed relative to a default signature, potentially removing text placed immediately above it, as noted by Xink Support.
- Default signature settings: Documentation often details how to properly set a default signature for new emails, replies, and forwards to ensure consistent application. Misconfiguration here can mean the signature simply isn't included.
- Embedded versus linked images: Guides often differentiate between embedding images directly (which can increase email size and sometimes trigger filters) and linking to externally hosted images (often preferred for deliverability).
- Platform-specific nuances: Documentation from providers like HubSpot, Adobe, or email signature services highlights unique configuration steps or potential conflicts that can arise when integrating signatures with their systems.
Key considerations
- Adhere to HTML standards: Ensure your signature's HTML is clean, simple, and follows web standards to prevent rendering errors or filter triggers. This also ties into overall email authentication like DMARC, SPF, and DKIM.
- Test across clients: Send test emails to a variety of email clients (Outlook, Gmail, Apple Mail) and devices (desktop, mobile) to confirm consistent rendering and delivery.
- Review signature setup guides: Consult the specific documentation for your email client or signature management software to ensure all settings are correctly configured. Microsoft users should review how to comply with Outlook's new sender requirements.
- Avoid excessive links or trackers: While not always explicitly stated as a deliverability risk, documentation implicitly encourages efficient and relevant linking, which aids in avoiding spam triggers.
- Understand attachment handling: Be aware that certain email clients or server configurations might convert inline images into attachments, which can sometimes impact perceived spamminess and user experience.
Technical article
HubSpot Community documentation details the process for updating team email signatures, typically found under Menu > Conversations > Inbox, then navigating to settings icon > Channels. This structured approach is designed to ensure consistent application across all team members. This indicates that signature management is often integrated into the platform's broader communication settings, emphasizing that proper configuration within the tool is key to avoiding issues and ensuring signature visibility.
Technical article
MySignature documentation advises users to verify that their email client's format is set to HTML when composing new emails. It explicitly states that if emails are sent as plain text, the signature, especially one with images or rich formatting, will not display correctly. This highlights a fundamental requirement for visual signatures. Misconfiguring this setting can lead to the signature being entirely absent or appearing as unformatted text, causing perceived delivery failure of the signature content.
Related resources
11 resources
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