It’s a common question among email marketers and senders: Can images in emails cause them to go to spam? The short answer is yes, they can, but it's rarely as simple as just having an image. Email spam filters, like those used by Gmail and Outlook, are sophisticated. They evaluate a multitude of factors to determine an email's legitimacy, and images are just one piece of that complex puzzle.
My experience has shown that it's more about how images are used, rather than their mere presence. Certain practices involving images can significantly increase the chances of your email being flagged as spam or junk. Understanding these common pitfalls and adopting best practices can help ensure your messages consistently reach the inbox.
The nuanced relationship between images and spam filters
While an image itself doesn't inherently trigger a spam filter, the context and implementation surrounding it can. Spam filters analyze various elements of an email to assign a spam score. A higher score increases the likelihood of your email landing in the spam folder (or being blocklisted). Images contribute to this score based on factors like their ratio to text, their hosting source, and how they are embedded.
One of the primary concerns is when emails are composed almost entirely of images with very little accompanying text. This practice is often employed by spammers to hide malicious content or evade text-based filters that scan for certain keywords. Because spam filters can't read the content within images, an image-only email raises a red flag, prompting closer scrutiny. For this reason, it is important to understand how image-only emails affect deliverability.
It's also crucial to remember that inbox providers consider your overall sender reputation. Even with perfectly optimized images, a poor sender reputation can overshadow your efforts, leading to spam folder placement. This includes factors like being on a blocklist (or blacklist), high complaint rates, or sending to invalid addresses.
Common ways images trigger spam filters
Several image-related issues can negatively impact your email deliverability. Being aware of these can help you fine-tune your email campaigns.
Image-heavy emails (low text-to-image ratio)
Emails with a disproportionate amount of images compared to text are often viewed suspiciously. This is a common tactic used by spammers to embed deceptive content that text filters cannot easily scan. Some ISPs (Internet Service Providers) actively flag such emails.
Images hosted on poor reputation domains
If the domain where your images are hosted has a poor reputation or is known for sending spam, it can directly impact your email's deliverability. Spam filters check the reputation of all linked domains within an email, including those hosting images. This means that even if your sending domain has a good reputation, a problematic image-hosting domain can cause your email to be blocklisted (or blacklisted).
Large image file sizes
Emails with excessively large image files can lead to slower loading times and a poor user experience. More importantly, they can trigger spam filters which view large attachments or file sizes with suspicion, potentially signaling a malware attempt. This is especially true if you are embedding images directly instead of linking to them.
Missing or generic alt text
Alt text (alternative text) provides a description for an image if it fails to load or for visually impaired recipients using screen readers. Missing or generic alt text can make your email seem less legitimate to spam filters because it signals a lack of proper HTML structure and accessibility considerations, which spammers often disregard.
Another specific issue I've encountered is when images contain suspicious links or are themselves linked to questionable URLs. Spam filters can detect malicious links within an email's HTML, even if they are embedded within an image or used as the click-through target for an image. Using image-only emails to deliver a message often goes hand-in-hand with deceptive content, which is why it's a major red flag.
Best practices for images in emails
To prevent images from negatively affecting your email deliverability, adhere to a few key best practices. These strategies help create emails that are both engaging for your audience and friendly for spam filters.
Optimize image sizes: Always compress images to reduce file size without sacrificing quality. This improves loading times and reduces the likelihood of being flagged for large attachments.
Use descriptive alt text: Provide clear, concise, and descriptive alt text for every image. This serves as a fallback if images don't load and helps spam filters understand the image content. For example, instead of image1.jpg, use Logo of Suped.
Maintain a balanced text-to-image ratio: Aim for a good balance between text and images. While there's no magic number, generally, emails that are predominantly text with supporting images perform better. You can read more about the impact of image-to-text ratio on deliverability.
Host images on reputable domains: Use a reliable and well-regarded Content Delivery Network (CDN) or your own trusted domain to host images. Avoid free or questionable image hosting services.
I often use this structure for my images:
Example of well-formatted image HTMLhtml
<img src="https://example.com/images/suped-logo.png" alt="Suped company logo" width="200" height="50">
Testing your emails before sending a large campaign is paramount. Many tools allow you to preview how your emails will render across different clients and check their spam score. This can highlight potential issues with your image usage or HTML structure before they affect your deliverability.
The holistic approach to email deliverability
While image best practices are important, they are only one part of a robust email deliverability strategy. The overarching factor influencing whether your emails land in the inbox or spam folder is your sender reputation. A strong sender reputation signals to ISPs that you are a legitimate and trustworthy sender.
This reputation is built over time through consistent positive sending behavior. This includes maintaining clean email lists, avoiding spam traps, authenticating your emails properly with SPF, DKIM, and DMARC, and sending relevant content that recipients engage with. Even if your email has perfect images, a history of poor engagement or high complaint rates can send it directly to the junk folder.
Therefore, I always advise a holistic approach to email deliverability. Focus not just on individual elements like images, but on the entire sending ecosystem. This includes technical configurations, content quality, recipient engagement, and proactively troubleshooting deliverability issues. Maintaining a healthy email program minimizes the risk of images (or any other component) inadvertently triggering spam filters.
Views from the trenches
Best practices
Always include relevant alt text for all images to ensure accessibility and provide context to filters.
Maintain a healthy balance of text and images in your emails to avoid triggering spam filters.
Host your images on reputable content delivery networks (CDNs) or trusted, high-reputation domains.
Regularly test your email designs across various email clients to identify rendering and deliverability issues.
Monitor your sender reputation and implement DMARC, DKIM, and SPF for proper email authentication.
Common pitfalls
Sending image-only emails where the entire message content is contained within one large image.
Using images with generic filenames or missing alt text, making them less readable by spam filters.
Embedding images directly into the email body instead of linking to externally hosted images.
Hosting images on free, low-reputation, or shared domains that might be associated with spam activity.
Ignoring the overall email HTML structure, even if images themselves are optimized.
Expert tips
Spam filters don't just look at images; they analyze the entire email's content and structure.
A sudden change in email structure, like adding background images, can affect deliverability.
Image attributes, including hidden text or metadata, can influence how spam filters perceive them.
Even if one part of your email infrastructure is healthy, a weak link elsewhere can cause problems.
Continuously test and iterate on your email designs to find what works best for your specific audience.
Expert view
Expert from Email Geeks says that images can cause emails to go to spam, but it is a very broad question with many contributing factors.
2021-09-16 - Email Geeks
Expert view
Expert from Email Geeks says that if an image is hosted on a domain with a poor reputation, it is highly likely to cause an email to be marked as spam.
2021-09-16 - Email Geeks
The bigger picture
Images in emails can indeed contribute to them being marked as spam, but it's not a standalone factor. Instead, it's often a combination of how images are implemented, the ratio of images to text, the reputation of image hosting domains, and the overall sender reputation that determines deliverability. My approach is to always focus on a comprehensive deliverability strategy that includes optimizing images, authenticating emails, and maintaining a positive sending history.
By following best practices for image usage and maintaining strong email hygiene, you can significantly reduce the risk of your messages going to the spam folder. Remember, a single problematic element, like a poorly optimized image, can sometimes be the tipping point, but it's always part of a larger picture that spam filters evaluate.
Gmail and 
Outlook, are sophisticated. They evaluate a multitude of factors to determine an email's legitimacy, and images are just one piece of that complex puzzle.
