Summary
Email code quality and size significantly impact deliverability. While code weight isn't the only factor, poorly structured, bloated, or error-filled code increases the likelihood of emails landing in spam folders, rendering incorrectly across devices, and causing truncation. Gmail truncates emails over 102kb. Best practices include clean, concise code, adherence to coding standards (inline CSS), optimized images, and platform testing. Missing alt tags and HTML errors can also affect deliverability. Spammers may use specific code patterns, and association with these can trigger spam filters. Ultimately, a professional-looking email with clean code enhances user experience, reducing spam complaints, and preserving domain reputation.
Key findings
- Gmail Truncation: Gmail truncates emails larger than 102KB, impacting user experience.
- Spam Code Association: Spam filters may identify code patterns frequently used by spammers.
- Bloated Code: Bloated code increases the likelihood of emails being flagged as spam and can cause rendering issues.
- HTML Errors: HTML errors increase spam scores, leading to lower deliverability rates.
- Rendering Issues: Poorly coded emails may not display correctly on all devices, triggering spam filters.
- Reputation Damage: Repeatedly being flagged as spam damages domain/server reputation.
- Image Size Matters: Large image size can also contribute to deliverability problems because of download issues with the email clients of the recipient.
- The cleaner the code, the better: The cleaner the code, the easier time spam filters will have understanding what the email is about
- Broken rendering costs money: Poor rendering means a user is more likely to mark as spam, and that will cost money.
Key considerations
- Code Optimization: Keep HTML code concise and efficient, removing unnecessary elements to stay below size thresholds.
- Image Optimization: Optimize images for size and ensure appropriate alt text is used.
- Error Prevention: Validate and fix HTML errors using available tools to reduce spam scores.
- Coding Practices: Use best practices like inline CSS, avoiding excessive images, and ensuring clean, well-structured code.
- Platform Testing: Test emails across different email clients and devices to ensure proper rendering.
- Monitor Reputation: Actively monitor domain/server reputation to identify and address deliverability issues.
- ALT Tags: Missing ALT tags on images negatively affects deliverability
What email marketers say
12 marketer opinions
Email code quality and size significantly impact email deliverability. Bloated, poorly structured, or error-filled code increases the likelihood of emails landing in spam folders and rendering incorrectly across different email clients. Large email sizes can also lead to truncation by email providers like Gmail. Clean, concise code, adherence to best practices (like inline CSS), and thorough testing improve deliverability by ensuring proper rendering, avoiding spam filters, and providing a better user experience.
Key opinions
- Gmail Truncation: Gmail truncates emails larger than 102kb, which can negatively impact the user experience.
- HTML Errors: HTML errors increase spam scores, leading to lower deliverability rates. Tools like GlockApps and Email on Acid can help identify these errors.
- Bloated Code: Bloated code increases the likelihood of emails being flagged as spam and can cause rendering issues, particularly on mobile devices.
- Rendering Issues: Poorly coded emails may not display correctly on all devices, triggering spam filters and potentially leading users to mark emails as spam.
- Code Clarity: Cleaner HTML code allows spam filters to better understand the email's content, improving deliverability.
Key considerations
- Code Optimization: Keep HTML code concise and efficient, removing unnecessary elements to stay below size thresholds and avoid truncation.
- Error Prevention: Validate and fix HTML errors using available tools to reduce spam scores and ensure proper rendering.
- Coding Practices: Use best practices like inline CSS, avoid excessive images, and ensure clean, well-structured code to improve compatibility and avoid spam filters.
- Platform Testing: Test emails across different email clients and devices to ensure proper rendering and user experience.
- ALT Tags: Make sure all images have valid ALT tags.
Marketer view
Email marketer from HubSpot shares that poorly coded emails may not display correctly on all devices and can trigger spam filters. Ensure your code is well-structured and follows email coding best practices.
16 Nov 2024 - HubSpot
Marketer view
Email marketer from Email Geeks shares that things like missing alt tags can affect deliverability, and HTML errors can affect deliverability. Suggests using a tool like GlockApps to check for errors.
24 Jul 2021 - Email Geeks
What the experts say
4 expert opinions
Email code quality and size can significantly impact deliverability, though not always in obvious ways. While heavier code itself might not be the primary issue, the association of certain coding styles with spam can trigger filters. Furthermore, poorly structured or messy code, excessive use of images, and large image sizes can lead to emails being flagged as unprofessional or spam, ultimately damaging your domain reputation and deliverability.
Key opinions
- Spam Code Association: Spam filters may identify code patterns frequently used by spammers, leading to misclassification of legitimate emails.
- Large Image Impact: Large images can be problematic because recipients need to download them, and if images are blocked, the entire email's message may be missed.
- Unprofessional Appearance: Messy code and poor coding practices can make an email look unprofessional, which can hurt the domain's deliverability.
- Reputation Damage: Repeatedly being flagged as spam damages your domain and server reputation, reducing the likelihood of future emails reaching the inbox.
Key considerations
- Code Review: Implement code review and testing processes to ensure email code is clean, professional, and avoids common spam triggers.
- Image Optimization: Optimize images for size and ensure appropriate alt text is used to maintain message integrity even when images are blocked.
- Monitor Reputation: Actively monitor your domain and server reputation to identify and address any deliverability issues promptly.
- Avoid Triggers: Be aware of coding techniques and content choices that are commonly associated with spam to avoid triggering filters.
Expert view
Expert from Spamresource explains that if your email campaign is flagged as spam too frequently, it will damage your domain and your server. The more you damage these, the less likely people will be to receive your emails.
31 Dec 2021 - Spamresource
Expert view
Expert from Word to the Wise explains that one large image in your email requires a receiver to download a large file. If their spam filter blocks images, they may not see the rest of your content and be more likely to mark you as spam.
15 Nov 2021 - Word to the Wise
What the documentation says
4 technical articles
Email deliverability is affected by email size and adherence to internet standards. Gmail truncates emails exceeding 102 KB, potentially harming user experience. Other email clients also have size limits. Following the Internet Engineering Task Force's standards for message formatting ensures proper parsing by email servers, reducing the risk of emails being marked as spam.
Key findings
- Gmail Truncation: Gmail truncates emails larger than 102 KB.
- Size Limits: Large email sizes can lead to clipping in Gmail and other email clients, impacting user experience.
- Attachment Limits: Outlook has limitations on maximum email size and attachments; exceeding them causes errors.
- Standard Compliance: Adhering to IETF standards ensures proper email parsing and reduces spam risk.
Key considerations
- Optimize Size: Keep email size below 102 KB to avoid Gmail truncation and other client limitations.
- Content Strategies: If you cannot reduce email size, consider clipping messages or linking to external content.
- Attachment Awareness: Be mindful of attachment sizes and limits to prevent sending or receiving errors.
- Follow Standards: Adhere to the IETF's standards for Internet message formatting.
Technical article
Documentation from Google Workspace Admin Help explains that Gmail truncates messages larger than 102 KB. It is recommended to clip larger messages.
10 Jan 2022 - Google Workspace Admin Help
Technical article
Documentation from Microsoft Support explains that there are limitations to the maximum email size and attachments supported by Outlook, exceeding this limit will cause sending or receiving errors. Check the official documentation for the latest maximums.
30 Mar 2025 - Microsoft Support
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