Summary
Email file size and the way images are hosted significantly influence Gmail deliverability. Larger email sizes can lead to slower loading times and trigger spam filters, potentially causing emails to be clipped or routed to the spam folder. The domains used for hosting images also play a crucial role, as Gmail heavily considers the reputation of all domains present within an email, including image URLs. Understanding these factors is key to optimizing your email campaigns for better inbox placement.
Key findings
- HTML size limit: Emails with HTML exceeding 102KB are prone to clipping in Gmail, which negatively impacts recipient experience.
- Image size impact: Large image files, often exceeding 100KB each, can increase the overall email size and affect deliverability.
- Domain reputation: Gmail extensively evaluates the domain reputation of all domains within an email, including those hosting images.
- Hosting location: Using unfamiliar or shared domains, such as generic S3 buckets, for image hosting can adversely affect email deliverability and sender reputation. Consider reviewing our guide on S3 buckets and custom domains.
Key considerations
- Optimize image sizes: Compress images to reduce file size without compromising quality, ensuring they load quickly.
- Monitor HTML size: Keep your email's HTML code under 100-102KB to prevent clipping and improve overall deliverability. Learn more about email file sizes and deliverability.
- Consistent image hosting: Host your images on a reputable domain with a strong sender reputation to build trust with internet service providers (ISPs).
- Test templates: Regularly test your email templates across various email clients, including Gmail, to identify and address any deliverability issues related to file size or image hosting.
What email marketers say
Email marketers often encounter deliverability challenges, particularly with Gmail, that can be linked to email file size and image hosting practices. They frequently discuss the direct impact of HTML and image sizes on inbox placement and user experience. A common concern is ensuring that image hosting domains do not negatively affect sender reputation, especially when using third-party services like S3 buckets or CDNs.
Key opinions
- File size concerns: Marketers frequently question if their email file size, particularly when exceeding certain thresholds like 102KB, contributes to deliverability problems.
- Image size impact: There's a strong perception that accidentally using large image files (e.g., over 100KB) can directly lead to reduced inbox placement.
- Image hosting domain: Many marketers identify the domain used for image links as a critical factor, noting that unknown or less reputable domains can severely impact delivery.
- Sudden drops: Experiencing sudden, unexplained drops in Gmail deliverability often prompts marketers to investigate file size or code-related issues.
Key considerations
- HTML clipping awareness: Marketers are advised to be aware of HTML clipping (which usually occurs around 102KB in Gmail) as a visible sign of excessive email size.
- Consistent hosting: Even if image links are hosted consistently, their domain's reputation remains a key deliverability factor. Review best practices for email images.
- Template re-use: A common strategy is to test with previously high-performing templates, ensuring the same image domains are used to isolate variables. This can help identify if new templates are causing issues, as discussed in our guide on HTML email size impacts.
- Image compression: Prioritizing image compression is critical to reduce overall email size and improve loading times for recipients.
Marketer view
Marketer from Email Geeks suggests investigating email file size and image dimensions as potential contributors to fluctuating Gmail deliverability rates, especially when sudden drops occur.
Marketer view
Email Development expert from Email on Acid states that an email file size around 100KB is generally safe for inbox delivery across major providers like Gmail, Yahoo, and Outlook.
What the experts say
Email deliverability experts consistently highlight the critical role of email file size and image hosting in ensuring messages reach the inbox. Their insights often emphasize that major mailbox providers, like Gmail, employ sophisticated spam filters that scrutinize not only content but also technical elements such as total email size and the reputation of linked domains. They underscore the importance of optimizing these aspects to avoid blacklists, improve sender reputation, and prevent message clipping.
Key opinions
- Image size thresholds: Experts advise that image sizes over 100KB can negatively impact email delivery rates.
- Unknown image domains: Using image links with domains that lack established reputation (e.g., generic S3 buckets) is a significant factor that can trigger spam filters and hinder deliverability.
- Domain reputation importance: Gmail heavily relies on the domain reputation of every URL within an email, including those for images, to assess its trustworthiness.
- Return-path domain: The return-path domain is also subject to scrutiny by ISPs, and its reputation is critical for deliverability.
Key considerations
- Comprehensive domain review: It is crucial to examine the reputation of all domains appearing in your email messages, including CDN hosted image domains, to ensure optimal inbox placement.
- Template testing: To diagnose deliverability issues, testing new templates against old ones with proven performance can help pinpoint problematic elements.
- Shared domain analysis: Pay close attention to any shared domains used in your email, including the return-path domain, as these significantly impact deliverability.
- Image optimization strategy: Implement a robust strategy for image optimization and hosting to maintain high deliverability standards, avoiding excessively large files.
Expert view
Expert from Email Geeks indicates that HTML size under 102KB prevents clipping, and warns that large image sizes (over 100KB) and unknown image hosting domains like S3 buckets can negatively impact deliverability.
Expert view
Expert from SpamResource.com notes that email service providers often apply file size limits, and exceeding these can lead to rejection or lower inbox placement.
What the documentation says
Official documentation and research consistently underscore the importance of email file size and image hosting practices for deliverability. They often define recommended size limits for both HTML and images, explaining how exceeding these can lead to negative outcomes like email clipping, rejection by servers, or flagging by spam filters. Furthermore, these resources frequently detail how the choice of image hosting and its associated domain reputation directly influence an email's ability to reach the inbox, impacting overall deliverability and user experience.
Key findings
- HTML file size limits: Documentation confirms that HTML email file sizes should ideally be 100KB or less to maximize inbox placement and avoid clipping issues, particularly with Gmail.
- Image contribution: Large image files are a primary contributor to increased email size, which can slow load times and affect engagement.
- Spam filter triggers: Excessively large email files, often due to unoptimized images, are identified as a factor that can trigger spam filters.
- Server rejection: Some email servers may reject messages that are deemed too large, leading to bounce backs.
Key considerations
- Overall size optimization: It's essential to optimize the total size of your emails, including both HTML and images, to prevent deliverability issues. This is also covered in our guide on code quality and size.
- Image compression techniques: Utilize efficient image compression techniques to reduce file sizes without noticeable quality degradation. Consider the impact of GIFs and their sizes on email deliverability.
- Image-to-text ratio: While not directly related to file size, an excessive reliance on images without sufficient text can also raise red flags with spam filters.
- User experience: Beyond deliverability, large file sizes lead to slower load times, negatively impacting recipient engagement and overall user experience. More information can be found on email file size limits.
Technical article
Mailchimp documentation outlines that email file size limits refer to the maximum attachment size, with email service providers imposing these restrictions.
Technical article
Campaign Refinery documentation states that longer and heavier emails can result in negative consequences, including slower loading times and poorer deliverability.
Related resources
14 resources
Related pages
How do S3 buckets and custom domains for image hosting affect email deliverability and reputation?
How does self-hosting email images affect deliverability?
How do HTML email size, TLD, attachments, and domain reputation affect deliverability and open rates?
How does email code quality and size impact email deliverability?
How do email image sizes affect deliverability and Gmail promotions tab placement?
How does the hostname used for image hosting affect email deliverability?
Does using a different domain for CDN hosted images in emails affect deliverability?
How to protect email deliverability for image-only emails?
Does a high image to text ratio affect email deliverability and spam filtering?
Why Your Emails Are Going to Spam in 2024 and How to Fix It
