Summary
Images in emails can significantly impact deliverability, potentially causing them to land in spam folders. Multiple factors contribute, including the image's hosting domain reputation, the text within the image, excessive image size, a high image-to-text ratio, missing or irrelevant alt text, broken images, improper embedding or linking methods, poorly implemented CID images, use of tracking pixels, and rendering issues. Machine learning filters evaluate everything in the email, making proper formatting, optimization, and mindful implementation essential to avoid triggering spam filters and maintain a positive sender reputation.
Key findings
- Image Hosting: Hosting images on domains with poor reputations can negatively affect deliverability.
- Image Attributes: The text within an image and its attributes can impact spam filters.
- Image Size: Excessively large, unoptimized images trigger spam filters due to slow loading and suspicion.
- Image-to-Text Ratio: A high image-to-text ratio can increase the spam score.
- Alt Text: Missing or irrelevant alt text makes emails look less legitimate and impacts accessibility.
- Broken Images: Broken images make emails look unprofessional and trigger spam filters.
- Rendering Issues: Rendering issues with background images can raise red flags.
- CID Images: Improperly implemented CID images can be flagged as suspicious.
- Tracking Pixels: Using tracking pixels can be detected and penalized by spam filters.
- ML Evaluation: Everything in an email is evaluated by machine learning filters.
- Image Linking: Linking directly to images can be problematic as loading is often blocked and may trigger flags.
Key considerations
- Reputable Hosting: Use reputable domains for image hosting to maintain a good sender reputation.
- Optimize Image Attributes: Carefully consider text within images and optimize image attributes.
- Optimize Image Size: Optimize images for size to improve loading times and user experience.
- Maintain Text Balance: Maintain a balanced image-to-text ratio.
- Implement Alt Text: Always include descriptive alt text for accessibility and legitimacy.
- Avoid Broken Images: Regularly check emails for broken images.
- Test Rendering: Test how background images render across different email clients.
- Implement CID Carefully: Implement CID images correctly.
- Use Tracking Pixels Cautiously: Be cautious when using tracking pixels.
- Email Elements: Be mindful of all email elements.
- Embedding vs Linking: Carefully consider the implications of embedding vs linking to images.
What email marketers say
11 marketer opinions
Images in emails can significantly impact deliverability and potentially cause emails to land in spam folders. Factors contributing to this include large image sizes, poor image hosting reputation, high image-to-text ratio, missing or irrelevant alt text, broken images, and the use of tracking pixels. Even rendering issues with background images and improper implementation of CID images can raise red flags with spam filters. Ultimately, it is important to carefully optimize images to avoid negatively affecting sender reputation and user experience.
Key opinions
- Image Size: Very large, unoptimized images can trigger spam filters due to slow loading times and perceived suspiciousness.
- Image Hosting: Hosting images on domains with poor reputations can negatively impact email deliverability.
- Image-to-Text Ratio: A high image-to-text ratio can increase spam scores.
- Alt Text: Missing or irrelevant alt text can make emails seem less legitimate to spam filters and impacts accessibility.
- Broken Images: Broken images can negatively impact deliverability by signaling unprofessionalism.
- Background Images: Rendering issues with background images across different email clients can trigger spam filters.
- CID Images: Improperly implemented CID (Content-ID) images can be flagged as suspicious.
- Tracking Pixels: The use of tracking pixels can be detected and penalized by some spam filters.
Key considerations
- Optimize Images: Ensure images are optimized for size and dimensions to reduce loading times and improve user experience.
- Use Reputable Hosting: Host images on reputable domains with good sender reputations.
- Maintain Text Balance: Maintain a balanced image-to-text ratio to avoid triggering spam filters.
- Implement Alt Text: Always include descriptive alt text for all images to enhance accessibility and legitimacy.
- Avoid Broken Images: Regularly check emails for broken images to maintain a professional appearance.
- Use Background Images Sparingly: Be mindful of how background images render and test across different email clients.
- Implement CID Properly: If using CID images, ensure they are implemented correctly to avoid triggering spam filters.
- Use Tracking Pixels Carefully: Be cautious when using tracking pixels, as some spam filters are designed to detect and penalize them.
Marketer view
Email marketer from StackOverflow warns that using CID (Content-ID) images, especially if improperly implemented, can be flagged as suspicious and lead to deliverability problems.
14 Nov 2024 - StackOverflow
Marketer view
Email marketer from Email Geeks shares that the text on an image can impact spam filters by changing image attributes.
22 Feb 2022 - Email Geeks
What the experts say
6 expert opinions
Images in emails can contribute to emails landing in spam. Factors include hosting images on domains with poor reputations, using excessively large images without optimization, failing to provide descriptive alt tags, and linking directly to images instead of embedding them. Email content is evaluated by machine learning filters and improperly implemented elements could affect deliverability.
Key opinions
- Image Hosting Reputation: Hosting images on domains with poor reputations can lead to emails being marked as spam.
- Image Size & Optimization: Excessively large, unoptimized images contribute to triggering spam filters due to slow loading times and negative user experience.
- Alt Tags: Failing to provide descriptive alt tags makes emails inaccessible and can negatively impact sender reputation, potentially triggering spam filters.
- Linked vs. Embedded Images: Linking directly to images hosted on a server can be problematic as many email clients block external image loading.
- ML Evaluation: Everything in an email, including images and HTML code, is evaluated by machine learning filters for spam detection.
Key considerations
- Reputable Hosting: Use reputable domains for image hosting to maintain a good sender reputation.
- Optimize Image Size: Optimize images to reduce file size and improve loading times.
- Descriptive Alt Tags: Provide descriptive alt tags for all images to enhance accessibility and avoid potential spam triggers.
- Embedding vs. Linking: Embed images directly in the email rather than linking to external sources to ensure visibility.
- Email Elements: Take all the elements in an email into account and ensure the email is properly formatted.
Expert view
Expert from Word to the Wise shares that linking directly to images hosted on a server, rather than embedding them in the email, can be problematic. Many email clients block external image loading by default, and depending on how it's implemented it could raise deliverability flags.
2 Jan 2025 - Word to the Wise
Expert view
Expert from Email Geeks explains that anything in the email is evaluated by machine learning (ML) filters.
19 Oct 2021 - Email Geeks
What the documentation says
3 technical articles
Email servers scrutinize the structure and content of emails, including how images are embedded. Improperly formatted images can lead to parsing errors and spam classification. Using images in a way that triggers spam filters can contribute to exceeding spam rate thresholds, negatively impacting deliverability. Content filters analyze images, and their properties contribute to the overall spam score.
Key findings
- Email Structure: The structure and content of the email body, including image embedding, are scrutinized by email servers.
- Spam Rate Thresholds: Exceeding spam rate thresholds, partly due to improper image use, negatively impacts deliverability.
- Content Filters: Content filters analyze images, and their properties contribute to the email's overall spam score.
- Improper Formatting: Improperly formatted images can cause errors and lead to spam classification.
Key considerations
- Proper Image Formatting: Ensure images are properly formatted to avoid parsing errors and potential spam classification.
- Monitor Spam Rate: Monitor spam rates and adjust image usage to stay below threshold levels.
- Optimize for Content Filters: Optimize images for content filters by following best practices for image size, alt text, and embedding methods.
- Image Properties: Be mindful of the properties of images and how they may affect the overall spam score.
Technical article
Documentation from Google explains that exceeding spam rate thresholds can negatively impact deliverability. Using images in a way that triggers spam filters contributes to the overall spam rate.
4 Oct 2024 - Google
Technical article
Documentation from Microsoft explains that their Smart Network Data Services (SNDS) uses content filters to identify potentially unwanted emails, and images are a part of this analysis. The properties of the images can contribute to the overall spam score.
20 Oct 2024 - Microsoft
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