Do X-Headers negatively impact email deliverability?

Email marketer from EmailToolTester responds that email deliverability is impacted by many factors, including but not limited to, sender reputation, authentication, content, and spam complaints. X-Headers are not mentioned specifically.

Email marketer from Postmark discusses best practices for email headers, focusing on standard headers like From, To, Subject, and Date, but does not specifically address X-Headers and their potential impact on deliverability.

Email marketer from Litmus explains that improving email deliverability depends on authentication, sending reputation, and avoiding spam triggers. X-Headers are not mentioned specifically.

Email marketer from Reddit shares that X-Headers can be used for tracking purposes, but should be used with caution. Be wary of header injection.

Marketer from Email Geeks explains that while X-headers were weighted in spam filters 20 years ago, believing they influence deliverability today is like 'reading tea leaves'.

Email marketer from Mailjet explains that some spam filters may look at X-Headers to identify spam. However, they are generally not as important as other factors like authentication, sender reputation, and content.

Email marketer from Stack Overflow answers question about how to properly inject X-Headers into emails. They share an example implementation for PHP using mail()

Marketer from Email Geeks suggests that while any element in an email *could* impact deliverability, it's unlikely a single minor data point will pull otherwise good email into spam. If a non-obvious data point is causing issues, the overall quality of the email's data points is likely not good to begin with.

Expert from Word to the Wise responds that X- headers can be valuable for internal tracking and analysis but emphasizes the importance of ensuring they do not violate email standards or introduce security vulnerabilities that spammers could exploit. Using them correctly and sparingly is recommended.

Expert from Spam Resource explains that using X-Headers for tracking purposes can present risks, especially if not implemented correctly. Malicious actors can potentially exploit vulnerabilities in custom headers to inject spam or phishing attempts.

Expert from Email Geeks shares that if a specific element is more common in spam than in legitimate emails, it could potentially be a signal for a filter.

Expert from Email Geeks responds that senders with good practices can use various tools and unusual elements, yet maintain good email delivery because their overall practices are strong. They note that some clients grasp at 'flimsy straws' instead of addressing the underlying problems with their practices.

Documentation from Microsoft explains how to use the Message Header Analyzer tool to get insights into the x-headers of emails.

Documentation from DKIM Proxy shares how to configure the proxy to add a DKIM signature to outbound email messages as an X-Header.

Documentation from cPanel responds with how to add custom X-Headers by editing the exim configuration files.

Documentation from RFC 6648 shares that the standard for adding X-Headers, and similar parameters, to standard protocols is now considered 'obsolete' and discouraged.