Summary
Attaching PDFs directly to emails can negatively affect deliverability due to increased email size, triggering spam filters, and potential infrastructure strain. The best practice is to host PDFs on a publicly accessible server and link to them in the email body. This improves user experience by avoiding downloads, reduces carbon footprint, and allows for tracking engagement on the website. Scanning outgoing mail for malware and being mindful of file size limitations are crucial for maintaining a positive sender reputation. Email services recommend using cloud storage for large files.
Key findings
- Deliverability Impact: PDF attachments increase email size, triggering spam filters and negatively impacting deliverability.
- Spam Filters: Attachments, especially unsolicited ones, can flag emails as potential spam or malware.
- Infrastructure Load: Large attachments strain infrastructure during DKIM signing and increase server load.
- Message Size Limitations: Exceeding message size limits leads to rejection or delays in delivery.
- Website Tracking: Linking to content allows for tracking user engagement on the website.
Key considerations
- Link, Don't Attach: Host PDFs on a publicly accessible server and include a link in the email body.
- Optimize File Size: Compress PDFs to minimize file size and reduce deliverability impact.
- Use Cloud Storage: Consider cloud storage services (Google Drive, OneDrive, Dropbox) for sharing very large files.
- Scan for Malware: Implement outbound scanning for potential malware in attachments.
- Check Size Limits: Be aware of file size limitations on your and the recipient's email servers.
What email marketers say
14 marketer opinions
Attaching PDFs directly to emails can negatively impact deliverability due to increased email size, triggering spam filters, and straining infrastructure. Best practices include hosting PDFs on a publicly accessible server and linking to them in the email body, optimizing file size, and using cloud storage services for large files. Linking also improves user experience and reduces the email's carbon footprint.
Key opinions
- Negative Impact on Deliverability: PDF attachments can harm email deliverability by increasing email size and triggering spam filters.
- Spam Trigger: Email clients often flag attachments, especially PDFs, as potential spam or malware.
- Infrastructure Strain: Large attachments can strain infrastructure due to DKIM signing and increased server load.
- User Experience: Linking to PDFs provides a better user experience by avoiding the need for recipients to download files.
- Carbon Footprint: Attaching large files increases the carbon footprint of emails due to increased data transfer and storage.
Key considerations
- Hosting and Linking: Host PDFs on a publicly accessible server and include a link in the email body.
- File Size Optimization: Compress PDFs to reduce file size and minimize deliverability impact.
- Cloud Storage: Use cloud storage services like Google Drive or Dropbox for large files.
- Contextual Links: Provide context around the link in the email body, explaining what the PDF contains.
- Recipient Customization: If PDFs are customized for each recipient, consider the impact on infrastructure and carbon footprint.
Marketer view
Email marketer from Gmass explains that attaching files can increase email size and trigger spam filters, therefore they recommend linking to the PDF instead.
6 Jan 2022 - Gmass
Marketer view
Email marketer from Hunter.io recommends to always compress attachments and consider sharing files via cloud storage services like Google Drive or Dropbox.
10 Jan 2025 - Hunter
What the experts say
4 expert opinions
Experts recommend avoiding email attachments due to their potential negative impact on sender reputation and deliverability. Directing recipients to a website provides more control, tracking capabilities, and the ability to manage content dynamically. Additionally, scanning outgoing emails for malware and being mindful of file size limitations are crucial for maintaining a positive sending reputation and avoiding rejections or delays. Linking to content is the preferred method, especially for unsolicited emails.
Key opinions
- Control and Tracking: Directing users to a website allows for better control over content and tracking of user engagement.
- Reputation Impact: Using attachments, especially unsolicited ones, can harm your sender reputation.
- Malware Risk: Attachments increase the risk of transmitting malware and impacting spam scores.
- Size Limitations: Large attachments can lead to emails being rejected or delayed due to file size limitations.
Key considerations
- Website Redirect: Prioritize linking to content on your website instead of attaching files.
- Malware Scanning: Implement outbound scanning for potential malware in attachments.
- File Size Awareness: Be aware of file size limitations on your and the recipient's email servers.
- Reputation Management: Avoid sending unsolicited emails with attachments to protect your sender reputation.
Expert view
Expert from Word to the Wise explains that using attachments in emails, especially unsolicited ones, is a bad practice and can harm your reputation. Providing a link to the content on your website is a preferred method.
24 Aug 2021 - Word to the Wise
Expert view
Expert from Email Geeks shares that you have more control when directing people back to a website, you can see who's actually requesting them and you can have them expire. Lots of benefits to not just putting them on the email (where you won't even get to register a click for engagement).
18 Jan 2025 - Email Geeks
What the documentation says
5 technical articles
Technical documentation indicates that email message size significantly impacts deliverability. Large attachments, such as PDFs, contribute to increased email size, potentially leading to rejection by servers or being flagged as spam. Services like Gmail and Outlook have specific attachment size limits and recommend utilizing cloud storage solutions like Google Drive or OneDrive for larger files to avoid delivery issues. Additionally, attachments can elevate spam scores due to their potential for disguising malware.
Key findings
- Message Size Matters: Email message size is a crucial factor affecting deliverability.
- Attachment Size Limits: Email services impose attachment size limits to prevent server overload and abuse.
- Cloud Storage Recommendation: Cloud storage services are recommended for sharing large files instead of attaching them directly to emails.
- Increased Spam Score: Attachments can increase an email's spam score, heightening the risk of being filtered.
Key considerations
- File Size Optimization: Optimize attachments for size to reduce the overall email size.
- Cloud Storage Integration: Utilize cloud storage services for sharing large files.
- Content Linking: Link to documents hosted online instead of directly attaching them to emails.
- Service Limits Awareness: Be aware of the attachment size limits enforced by your email service provider and the recipient's.
Technical article
Documentation from Litmus explains that overly large emails, often caused by attachments, can increase the likelihood of being flagged as spam. They suggest optimizing attachments for size or linking to them instead.
8 Apr 2025 - Litmus
Technical article
Documentation from RFC2476 specifies that message size is a major factor in deliverability, with some servers rejecting large emails. PDFs increase the overall size of emails.
19 Aug 2022 - RFC2476
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