Is linking to PDFs bad for email deliverability?

Key findings

• Distinction: Linking to a PDF is significantly different from attaching one. Direct attachments are far more likely to cause deliverability issues due to file size limits and malware scanning concerns.
• URL scanning: Email filters will scan the URL linked to, just as they would any other link. The reputation of the domain hosting the PDF is crucial.
• Domain aliases: Using domain aliases that redirect to a PDF file introduces another layer of scrutiny. If the redirect chain or the final destination domain has a poor reputation, it could impact deliverability. See our guide on how link redirects affect email reputation.
• Recipient environment: Organizations with stringent security measures, such as healthcare providers, often employ aggressive firewalls and email filters that may treat links to certain file types (including PDFs) with more suspicion, regardless of best practices for general recipients.

Key considerations

• Host reputation: Ensure the domain hosting your PDF files has a strong, positive reputation. This is critical for avoiding blocklists and spam folders.
• Security scanning: Understand that recipient email servers and security appliances will perform scans on all links, including those to PDFs, for potential malware or suspicious content. Even well-formed PDFs can sometimes be flagged if the scanner is overly cautious or if the PDF contains active elements that might be perceived as risky. According to Quora, PDF files can indeed be used as carriers for viruses or malware.
• Alternative methods: Consider presenting information directly within the email body or on a dedicated webpage rather than solely relying on PDF links, especially for critical information. This reduces reliance on the recipient's ability to access or trust external files.
• Monitoring: Implement robust email deliverability monitoring to track inbox placement, engagement, and any specific error messages from recipient domains. This helps identify if PDF links are indeed contributing to blocking issues in your target audience.

Key opinions

• Linking vs. attaching: The consensus is that attaching PDFs is problematic, but linking to them is generally fine, similar to any other link. If you're looking for strategies to improve deliverability, understanding why emails fail is a good starting point.
• Filter variations: Some specialized filter vendors or highly secure recipient environments (like hospitals) might have their own peculiar rules or increased sensitivity towards links to certain file types.
• Reputation of linked content: The deliverability impact of a PDF link largely depends on the reputation of the domain where the PDF is hosted. A clean, reputable domain is less likely to trigger flags. This ties into overall email domain reputation.

Key considerations

• Vendor advice: If an agency or a specific filter vendor indicates that linked PDFs are an issue, it suggests their filters (or the filters of your recipients) are indeed treating them as red flags. This advice should be taken seriously for those specific target audiences.
• Industry specifics: Industries with high security requirements, such as healthcare, finance, or government, frequently have highly configured and sometimes idiosyncratic email security systems. What works for consumer mail may not apply directly.
• Testing: For specific problematic recipients, conducting targeted tests with and without PDF links can help isolate the cause of deliverability issues. Utilize an email deliverability tester to diagnose these issues.
• Content presentation: Where possible, embed key information directly in the email or link to an HTML webpage instead of a PDF. If a PDF is essential, consider a clear, concise call-to-action to download it, framed positively.

Key opinions

• Link neutrality: From a core deliverability standpoint, a link to a PDF is generally treated no differently than any other link. The content type at the end of the link is less important than the reputation of the URL itself.
• B2B filter behavior: Business-to-business (B2B) email filters, especially in regulated sectors like healthcare, often differ from consumer-facing filters. They may implement advanced link rewriting, proxying, and intensive malware scanning. See our guide to technical solutions for deliverability.
• Attachment risks: Attaching PDFs carries significant risks, including tripping up malware scanners, regardless of the quality of the PDF creation software. This is a fundamental reason to prefer linking over attaching.
• HIPAA and privacy: Healthcare organizations may have additional technology and policies in place to deal with HIPAA and other health privacy regulations, which could influence how links (especially to documents containing sensitive info) are processed.

Key considerations

• Vendor specific filters: If a specific filter vendor is flagging PDF links, it's critical to understand their reasoning. Their filters are actively configured to treat these links as suspicious for their client base.
• Domain and IP reputation: Ensure the IP and domain hosting the PDF (and sending the email) maintain an excellent reputation. Blocklist monitoring is essential for this.
• User interaction: Focus on driving positive user interaction. If recipients consistently open and click safe PDF links, it can build trust with receiving servers. Conversely, if links lead to bad experiences (e.g., slow downloads, broken files), it can hurt reputation.
• URL structure: While general links are fine, complex URL structures, excessive parameters, or suspicious-looking URLs might contribute to filtering. Keeping URLs clean and straightforward is always a good practice, similar to how link shorteners can cause deliverability issues.

Key findings

• Malware vectors: PDF files, while commonly used, can be used as 'carriers or containers for viruses or malware,' meaning they can be a means to deliver malicious software. This inherent risk is why some filters are cautious, even about links. Review our page on why emails go to spam.
• Suspicious content: Attachments (and by extension, content linked to) can be flagged as malicious or suspicious, particularly if they exhibit characteristics associated with common phishing or malware distribution techniques.
• Link scrutiny: Email deliverability best practices indicate that links are always scrutinized. While the file type at the end of the link is a factor, the overall reputation and security of the URL are primary concerns. Consider secure HTTPS links.
• CAN-SPAM Act: The CAN-SPAM Act, relevant for commercial emails, focuses on clear identification, valid headers, and unsubscribe options, but does not specifically prohibit linking to PDF files. Its primary aim is to regulate commercial email content and ensure transparency.

Key considerations

• Security best practices: Ensure any PDFs you link to are created securely, free of macros or executable content, and hosted on a server with robust security measures and a valid SSL certificate. Regularly scan your hosted files for vulnerabilities.
• Domain reputation: Maintain a strong domain reputation for both sending emails and hosting content. A clean sending history and a reputable website hosting your PDFs contribute positively to deliverability.
• Transparency: Clearly state what the link leads to. Ambiguous or disguised links are more likely to be flagged by security systems and distrusted by recipients.
• File size and loading: While linking avoids email size limits, large linked PDFs can still affect the user experience due to slow loading times, which can indirectly impact engagement metrics. This is a common issue for email best practices.