Can email signatures, especially via Exclaimer, cause SPF or DKIM failures and impact email delivery?

Summary

Third-party email signature services, such as Exclaimer, can significantly impact email deliverability through several mechanisms. These services route emails through their servers, which can lead to SPF failures unless the SPF record is updated to include their sending servers. They can also alter email content, potentially invalidating DKIM signatures, and contribute to DMARC failures if SPF and DKIM are not properly configured. Furthermore, large signatures with embedded images increase email size, triggering spam filters. Receiving issues are unlikely related to signature services. Troubleshooting often requires detailed data about delivery failures. Properly managing DKIM signing post-signature insertion, optimizing signature size, and adhering to IT policies are crucial for maintaining deliverability. Forwarding, structural quirks, and non-whitelisted links also play roles.

Key findings

  • SPF Failures: Third-party signature services can cause SPF failures due to routing emails through their servers.
  • DKIM Invalidations: Altering email content through signature services can invalidate DKIM signatures.
  • DMARC Failures: Improper SPF and DKIM configuration can lead to DMARC failures and reduced deliverability.
  • Signature Size Issues: Large signatures with embedded images can trigger spam filters.
  • Forwarding Impacts SPF: Email forwarding can break SPF, causing authentication problems.
  • Whitelabeling Impact: Lack of whitelabeling Exclaimer links could negatively impact your deliverability

Key considerations

  • SPF Record Updates: Update SPF records to include the sending servers of the third-party email signature service.
  • DKIM Management: Ensure the signature service properly manages DKIM signing after signature insertion.
  • Optimize Signature Size: Optimize signature size by using linked images instead of embedded ones.
  • Monitor Authentication: Regularly monitor authentication reports to identify and address deliverability issues.
  • Gather Delivery Data: Gather detailed data on delivery failures for effective troubleshooting.
  • Evaluate IT Policies: Evaluate any IT policies such as blocking base64 encoded content.

What email marketers say
8Marketer opinions

Third-party email signature services can significantly impact email deliverability. Issues arise from rewriting emails, which can cause SPF and DKIM failures, ultimately leading to emails being marked as spam. Large signatures with embedded images can increase email size, triggering spam filters. Proper configuration of SPF and DKIM, optimizing signature size, and monitoring authentication reports are crucial. Alterations of email content by these services can invalidate DKIM signatures, necessitating solutions such as DKIM signing after signature insertion.

Key opinions

  • SPF/DKIM Failures: Third-party signature services can cause SPF and DKIM failures due to email rewriting.
  • Spam Marking: Emails with improperly configured signatures are more likely to be marked as spam.
  • Signature Size: Large signatures with embedded images can increase email size and trigger spam filters.
  • DKIM Invalidation: Email signature services can alter email content, invalidating DKIM signatures.

Key considerations

  • Proper Configuration: Ensure proper configuration of SPF and DKIM when using third-party signature services.
  • Optimize Size: Optimize signature size by using linked images instead of embedded ones.
  • Monitor Authentication: Regularly monitor authentication reports to identify and address deliverability issues.
  • DKIM Signing: Implement DKIM signing after the signature service has processed the message, or use a service that offers this feature.
  • Testing: Test email deliverability with and without signatures to assess impact.
Marketer view

Email marketer from StackOverflow explains the challenges of email signature services altering email content, which can invalidate DKIM signatures. Suggesting using a service that signs the email after signature insertion or implementing DomainKeys Identified Mail (DKIM) signing after the signature service has processed the message.

January 2024 - StackOverflow
Marketer view

Email marketer from Mailtrap.io shares that third-party email signatures can rewrite emails and cause authentication problems, potentially resulting in emails being marked as spam. Proper configuration of SPF and DKIM is crucial when using these services.

January 2024 - Mailtrap.io
Marketer view

Email marketer from the EmailGeeks Forum reported issues with email deliverability after implementing a new company-wide email signature through a third-party service. They found that the signatures were altering the email content in a way that invalidated DKIM signatures. The solution was to adjust the settings in the third-party service to ensure DKIM signing occurred after the signature was applied.

June 2023 - EmailGeeks Forum
Marketer view

Email marketer from DigitalMarketer explains that large image sizes in email signatures can lead to increased load times, contributing to poor user experiences. The author recommends optimizing image size to improve deliverability.

June 2022 - DigitalMarketer
Marketer view

Email marketer from Email on Acid explains how incorrect handling of email signatures by third-party services can impact deliverability by causing SPF and DKIM failures. Suggests regularly monitoring authentication reports.

February 2024 - Email on Acid
Marketer view

Email marketer from Litmus warns that overly complex or large email signatures can trigger spam filters. Suggests testing email deliverability with and without signatures to assess their impact.

August 2024 - Litmus
Marketer view

Email marketer from GMass.co explains that overly large email signatures, especially those with embedded images, can increase email size, potentially triggering spam filters. They recommend optimizing signature size and using linked images instead of embedded ones.

June 2024 - GMass.co
Marketer view

Email marketer from Reddit shares an experience where implementing a company-wide email signature solution led to SPF failures and emails landing in spam folders. They resolved the issue by ensuring the signature service was properly authorized in their SPF record.

December 2022 - Reddit

What the experts say
10Expert opinions

The use of email signature services like Exclaimer can introduce complexities affecting email deliverability. While Microsoft 365 reapplies DKIM after Exclaimer's processing, potential issues include DMARC failures if DMARC policy is set to reject and the service strips DKIM before forwarding. Structural issues and non-whitelisted links within signatures may also contribute to deliverability problems. Troubleshooting requires detailed data on delivery failures, and receiving issues are often unrelated to Exclaimer. IT policies, such as blocking base64 encoded content, might also impact email display. Proper DKIM management by the signature service and avoiding forwarding that breaks SPF are crucial for maintaining deliverability.

Key opinions

  • DKIM Reapplication: Microsoft 365 typically reapplies DKIM after Exclaimer processes emails.
  • DMARC Policy Impact: Stripping DKIM before forwarding with a 'p=reject' DMARC policy can cause deliverability issues.
  • Signature Structure: Janky email structures and non-whitelisted links in signatures may impact deliverability.
  • Limited Exclaimer Impact: Receiving issues are likely unrelated to Exclaimer Cloud.
  • SPF Breaks: Forwarding can break SPF, causing deliverability problems.

Key considerations

  • Data for Troubleshooting: Gather detailed data on delivery failures, including rejection messages and affected domains/IPs.
  • IT Policy Review: Check for IT policies that may impact email display, such as blocking base64 encoded content.
  • DKIM Management: Ensure the email signature service properly manages DKIM signing after signature insertion to avoid invalidation.
  • Avoid Forwarding Issues: Avoid forwarding that breaks SPF.
  • Whitelabeling: Whitelabel the signature domain.
Expert view

Expert from Email Geeks states that the ball is in IT’s court and there’s not really anything you can do without more detailed data on the delivery issues.

December 2021 - Email Geeks
Expert view

Expert from Email Geeks suggests that receiving issues are likely unrelated to Exclaimer Cloud.

January 2025 - Email Geeks
Expert view

Expert from Spamresource.com explains that forwarding can break SPF as it is a common cause of SPF failures when emails pass through multiple servers which are not authorised to send on behalf of the original domain.

April 2022 - Spam Resource
Expert view

Expert from Email Geeks suggests it could be an IT policy, such as blocking all base64 encoded content. He advises asking IT for a list of their policies.

April 2021 - Email Geeks
Expert view

Expert from Email Geeks explains “Exclaimer strips out the DKIM when it receives an email, but it is re-applied by Microsoft 365 after it has been processed by Exclaimer and before being sent to the recipient server.” and confirms Authentication looks fine and the problem is unlikely to be SPF or DKIM related.

September 2024 - Email Geeks
Expert view

Expert from Email Geeks explains that the email structure is a bit janky but that Microsoft is known for that. He mentions there are links to exclaimer.net in the email which are not whitelabeled, so if they're commonly used in unwanted email that could have an impact.

January 2022 - Email Geeks
Expert view

Expert from Word to the Wise explains that email signature services can alter email content, which can invalidate DKIM signatures if not handled correctly. Ensuring the signature service properly manages DKIM signing after signature insertion is crucial for maintaining deliverability.

December 2022 - Word to the Wise
Expert view

Expert from Email Geeks explains that if Exclaimer is stripping DKIM before forwarding, the problem is you're publishing p=reject and you're telling recipients to throw away mail after the authentication is removed. She confirms that DMARC is passing.

April 2022 - Email Geeks
Expert view

Expert from Email Geeks explains that providing specific details like domains, IP addresses, rejection messages, and involved blocklists would increase the odds of receiving helpful advice.

October 2022 - Email Geeks
Expert view

Expert from Email Geeks explains the next step is probably to find out more about the delivery failures. If the mail was rejected, look at the rejection message. If it was delivered to spam, ask a friendly recipient to ask their admin why it was.

April 2024 - Email Geeks

What the documentation says
5Technical articles

Email signatures, particularly those managed by third-party services like Exclaimer, can introduce complexities that affect email deliverability. A primary concern is SPF failures, as emails may appear to originate from unauthorized servers, necessitating SPF record updates to include the service's sending servers. Additionally, email forwarding and any modifications to message content post-DKIM signing can invalidate DKIM signatures. Proper configuration of SPF and DKIM is crucial to avoid DMARC failures and maintain deliverability, especially when using these services, and misconfigured DNS records related to email signatures can lead to deliverability issues.

Key findings

  • SPF Failures: Third-party email signature services can cause SPF failures as emails are routed through different servers.
  • DKIM Invalidations: Email forwarding and modifications to the message content after DKIM signing can invalidate the signature.
  • DMARC Failures: Incorrect SPF and DKIM configuration when using third-party services can lead to DMARC failures.
  • DNS Issues: Misconfigured DNS records related to email signatures can cause deliverability issues.

Key considerations

  • SPF Record Updates: Update SPF records to include the sending servers of the third-party email signature service.
  • DKIM Configuration: Ensure proper DKIM signing is implemented, considering modifications to the message content.
  • Authentication: Carefully configure SPF and DKIM to ensure proper authentication when using third-party services.
  • Avoid Forwarding: Avoid forwarding where possible to limit DKIM issues
Technical article

Documentation from DMARC.org highlights that using third-party services, including those that add email signatures, requires careful SPF configuration to ensure proper authentication. Failing to do so can result in DMARC failures and reduced deliverability.

October 2022 - DMARC.org
Technical article

Documentation from Exclaimer.com explains that when using a third-party email signature service like Exclaimer, emails are routed through their servers, potentially causing SPF failures because the email appears to originate from a different server than the domain's authorized sending sources. They recommend updating the SPF record to include Exclaimer's sending servers to resolve this issue.

August 2021 - Exclaimer.com
Technical article

Documentation from Microsoft.com explains that email forwarding can break DKIM signatures, especially if the forwarding server modifies the message content. This can lead to deliverability issues as the receiving server may fail to authenticate the email.

January 2023 - Microsoft.com
Technical article

Documentation from RFC Editor (RFC 6376) explains that any modification to an email message after it has been signed with DKIM can invalidate the signature, leading to authentication failures. This includes changes made by email signature services.

February 2024 - RFC Editor
Technical article

Documentation from AuthSMTP provides guidelines on how email signatures can impact email deliverability, especially when third-party services are used. Proper SPF and DKIM configuration is necessary to prevent authentication failures. The email signatures can cause issues if they are not configured correctly in DNS records.

June 2023 - AuthSMTP