Summary
Emails failing to deliver when including a signature can stem from a multitude of factors, encompassing technical configurations, signature content, and recipient-side actions. Key contributors include: incorrect SPF, DKIM, and DMARC settings; overly complex or non-compliant HTML; large image files or poor image-to-text ratio; links to low-reputation domains or URL shorteners; hosting images on unreliable servers; spam-triggering words; missing or misleading alt text; suspiciously formatted phone numbers; and excessive tracking parameters. Recipients blocking the sender is also a potential cause. Troubleshooting involves systematically isolating problematic elements, ensuring proper email authentication, adhering to HTML standards, optimizing image usage, and practicing caution with links and tracking.
Key findings
- Authentication Failures: Improperly configured SPF, DKIM, and DMARC records can lead to emails being rejected, especially when signatures are present.
- HTML Issues: Overly complex or non-compliant HTML in signatures triggers spam filters and causes rendering problems.
- Image Optimization: Large image files, missing alt text, and poor image-to-text ratios negatively impact deliverability.
- Link Reputation and Tracking: Links to low-reputation domains, use of URL shorteners, and excessive tracking parameters raise suspicion with spam filters.
- Hosting Reliability: Hosting images on unreliable or blacklisted servers results in emails being blocked.
- Content Issues: Spam-triggering words and suspiciously formatted phone numbers increase the likelihood of emails being filtered.
- Recipient Blocking: Recipients blocking the sender prevents email delivery.
Key considerations
- Configure Email Authentication: Ensure SPF, DKIM, and DMARC records are correctly configured for your domain.
- Simplify Signature HTML: Use simple, well-formatted HTML and avoid excessive CSS or JavaScript.
- Optimize Images: Reduce image file sizes, provide descriptive alt text, and maintain a balanced text-to-image ratio.
- Review Links and Tracking: Avoid linking to low-reputation domains, using URL shorteners, and including excessive tracking parameters.
- Use Reputable Hosting: Host signature images on reliable and reputable servers.
- Avoid Spammy Content: Refrain from using spam-triggering words and ensure phone numbers are formatted correctly.
- Check Blocked Sender Lists: Advise senders to confirm they aren't blocked by recipients and to remove and re-add contact if necessary.
- Isolate Elements: Testing the signature by removing elements to isolate any issues that can affect deliverability
What email marketers say
9 marketer opinions
Emails may not be delivered when including a signature due to various factors related to the signature's content, code, and associated links. Large image files, problematic HTML, links to low-reputation domains or URL shorteners, hosting images on blacklisted servers, spam-triggering words, missing image alt text, a poor image-to-text ratio, and even phone numbers formatted suspiciously can all lead to deliverability issues by triggering spam filters.
Key opinions
- Image Issues: Large image files in signatures increase email size and can trigger spam filters. Missing or misleading alt text can also be problematic.
- Link Reputation: Links to low-reputation domains or the use of URL shorteners in signatures are often flagged as suspicious by spam filters.
- HTML Code: Problematic or complex HTML code within the signature can cause deliverability issues. Simple HTML is preferred.
- Hosting Issues: Hosting images on unreliable or blacklisted servers can lead to emails being blocked.
- Spam Trigger Words: Certain words in signatures, particularly those related to sales, finance, or health, can trigger spam filters.
- Text-to-Image Ratio: A signature with too many images compared to text can negatively impact deliverability.
- Phone Number Formatting: Suspiciously formatted phone numbers in signatures can cause deliverability issues.
Key considerations
- Optimize Images: Reduce the file size of images in your signature without sacrificing quality.
- Check Link Reputation: Monitor the reputation of domains you link to in your signature and avoid using URL shorteners.
- Simplify HTML: Use simple, well-formatted HTML code for your signature.
- Use Reputable Hosting: Host images for your signature on reliable and reputable platforms.
- Avoid Spammy Language: Refrain from using overly promotional or suspicious language in your signature.
- Descriptive ALT Text: Include appropriate and useful ALT text for images in the signature.
- Maintain Balance: Ensure a reasonable text-to-image ratio.
- Phone Number Format: Ensure any phone number that is in the signature is formatted well
Marketer view
Email marketer from Mailchimp Resource Center explains that large image files in your email signature can increase the email's overall size, potentially causing it to be flagged as spam or rejected by some email servers. Optimize images to reduce file size without sacrificing quality.
18 Apr 2022 - Mailchimp Resource Center
Marketer view
Email marketer from Email on Acid shares that using URL shorteners (like bit.ly) in your email signature can negatively impact deliverability. Spam filters often flag shortened URLs as suspicious because they can mask the true destination of the link.
27 May 2023 - Email on Acid
What the experts say
5 expert opinions
When emails are not delivered with a signature, the cause often involves identifying problematic elements within the signature through a process of elimination. Experts suggest testing the signature by removing potentially problematic elements one at a time, such as phone numbers, domains, image hosts, URLs, or social tags. A key issue could be a destination URL with a bad reputation. Additionally, overly complex HTML, large images, unusual fonts, and excessive tracking parameters on links can contribute to deliverability problems by raising suspicion with spam filters.
Key opinions
- Problem Isolation: Deliverability issues from signatures often stem from a single problematic element that can be isolated through testing.
- Domain Reputation: The reputation of domains linked in signatures can significantly impact deliverability.
- Signature Complexity: Overly complex HTML, large images, and unusual fonts can negatively affect deliverability.
- Tracking Parameter Overuse: Excessive tracking parameters in signature links can trigger spam filters.
Key considerations
- Element Removal Testing: Systematically remove elements from the signature to pinpoint the cause of deliverability issues.
- Reputation Review: Ensure linked domains have a good reputation to avoid being flagged by spam filters.
- Keep it Simple: Opt for simple HTML, web-safe fonts, and appropriately sized images in signatures.
- Tracking Judiciously: Use tracking parameters sparingly to avoid raising suspicions.
Expert view
Expert from Email Geeks suspects the destination URL (<http://addictivedesign.ca|addictivedesign.ca>) in the signature might have a bad reputation, causing delivery issues.
7 Jul 2021 - Email Geeks
Expert view
Expert from Email Geeks recommends removing elements from the signature one at a time to identify the problematic element, suggesting the logo's host, URLs, or social tags could be the issue.
21 Sep 2022 - Email Geeks
What the documentation says
5 technical articles
Email deliverability issues when including a signature can arise from various technical configurations and recipient-side actions. These include recipients blocking the sender, improper SPF, DKIM, and DMARC configuration leading to failed email authentication, non-compliant HTML code in the signature triggering spam filters, incorrect DKIM record formatting, and exceeding the SPF record lookup limit. Addressing these issues involves ensuring proper email authentication setup, adhering to HTML standards, and managing SPF record complexity.
Key findings
- Recipient Blocking: Recipients accidentally adding senders to blocked lists can cause delivery failures.
- Email Authentication: Improper SPF, DKIM, and DMARC configuration leads to email rejections, especially with signatures.
- Non-Compliant HTML: Non-compliant HTML in signatures triggers spam filters.
- Incorrect DKIM: Incorrectly formatted DKIM records cause email authentication failures.
- SPF Record Limit: Exceeding the SPF record lookup limit causes SPF checks to fail, leading to email rejection.
Key considerations
- Check Blocked Lists: Advise senders to confirm they aren't blocked by recipients.
- Configure Authentication: Properly configure SPF, DKIM, and DMARC records for the sending domain.
- Adhere to Standards: Ensure the HTML code in the signature adheres to email standards and avoids excessive CSS or JavaScript.
- Validate DKIM: Use a DKIM validator to verify the DKIM record's correctness.
- Manage SPF Complexity: Keep the SPF record complexity within the lookup limit to avoid SPF check failures.
Technical article
Documentation from Microsoft Support explains that if the recipient has accidentally added the sender's email address or domain to their blocked sender list in Outlook, emails, including those with signatures, will be automatically moved to the Junk Email folder or rejected outright.
15 May 2024 - Microsoft Support
Technical article
Documentation from RFC Editor specifies that non-compliant HTML code in email signatures can cause rendering issues or trigger spam filters. Ensure your signature code adheres to email standards (e.g., avoiding excessive use of CSS or JavaScript).
9 Jun 2023 - RFC Editor
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