How to Survive Image Blocking

Aside from the usual hurdles marketers need to over come, like deliverability or creating the perfect content, there’s another issue to contend with – image blocking. Many people are blocking images in the HTML formatted messages they are receiving, this could be because it’s an email client’s default setting or it could be a recipient’s personal preference, and some people block HTML completely.

Here’s why…

Most email clients block HTML images. Whilst this can be frustrating from an email marketer’s point of view – there is a good reason for it.

When someone crafts a HTML email that includes images, the images either accompany the email, or they reside somewhere externally on the internet. When you open the email, in order to display the images, your email program must access the server to fetch the file.

When you choose to display the HTML images, your mail program will fetch the images and display them automatically, no matter where the email came from or who sent it. The images can be displayed even if the email is from a spammer.

Remember – every time you access a web page or an image from a website, the web server will ‘notice’. In this situation if a spammer sent the email, they would notice you had opened the email and accessed the image. They then know your email address is live, and that someone actually read it. As a result, they send that address more spam.

If you leave images blocked by default, then this doesn’t happen. Even if you open the email, the spammer won’t know, unless you choose to view the images.


In the past, Microsoft Outlook used Internet Explorer (Trident) as its rendering engine. However, due to rendering discrepancies between versions of Outlook, this was changed to Microsoft Word in the update in 2007.

Whilst Microsoft fixed the original issues, transferring the rendering engine to Word has caused a lot of new problems, and a lot of unhappy users. Microsoft Word is very poor at rendering HTML that wasn’t created in Word in the first place – creating another barrier for email marketers to overcome.

This issue with Outlook prompted a Twitter storm. Over 30,000 people tweeted their irritation at Microsoft and asked them to improve their standards in the next update.

We should now note that web-based email clients, like Gmail for example, uses the rendering engine of the user’s browser meaning you should make sure your email renders correctly in Internet Explorer and Firefox.

image blocking

Because of these problems when using Outlook to open emails, as a marketer you’ll face a few common issues that you need to take into account, especially if you’re sending lots of emails to Microsoft Outlook users.

1. Spacing – If you use double spacing, you may see additional line breaks between paragraphs. If you have a lot of content with images, you may see random white space. Outlook checks how your email would look when printed, and may add extra space above an image, as though it would need to be printed across two pages.

2. Fonts – If you’ve coded your own template make sure you set your font styles on the parent element of your text. If you set a font, then change it by highlighting the text, things may appear different in Outlook as it doesn’t follow standard conventions for regulating text conflicts.

3. Images – if you have added a large image and changed the dimensions in an ESP’s system, chances are Outlook will keep the image at the original size because Word rendering doesn’t handle resizing very well.

With 25 million users worldwide, chances are your campaign will be opened using Microsoft Outlook at some point – meaning you need to take these users into consideration too.

Best practices

According to a study by Merkle, a CRM agency, only 48% of email recipients see images automatically. Which mean the 52%, the majority, do not. So what happens to your email when the images are blocked? What are the best practices to ensure we’re optimising presentation?

From an email designer’s point of view, an email is successful when it meets these goals:

1. Retains visual integrity in the most frequently used email clients with images enabled.

2. Retains readability in the most common email clients with images disabled.

3. The email is readable to people with visual disabilities.

4. The email is low is weight for users on mobile devices.

5. The email is sent to a list of willing recipients.

6. The email passes common tests presented by spam filters.

When we look through this list we can see how important images are. If you depend on images to heavily it can lead to failures on many different levels. This means as an email designer, you need to prepare for a scenario in which images are disabled, but still portrays the same message and information.

Become a known sender

Almost every email client enables people to automatically display images when a message is from a known sender. A sender could be ‘known’ for a number of reasons – senders appearing in whitelists, or being added to contact lists or address books.

Gmail have recently started automatically displaying images in emails when you’ve received a message from that sender twice, just because the people in this group are likely to be people you know and trust. Of course this action can be reversed if you’d rather protect your inbox.

Your subscribers are subscribers for a reason – they’re happy to receive correspondence from you and want to continue receiving emails. With a couple of simple notifications you can increase your chances of success:

1. Ask a subscriber to add the email address to their address book – on the subscribe form – and explain why.

2. Create a double opt-in process. Send a plain text confirmation which includes a request to be added to a recipients address book and again explain why.

Telling a subscriber about this simple step will increase your chances of having the images enabled.

Alternatively larger senders could get an IP certification. Return Path offer a certification which ensures that your IP is placed on a whitelist and the images included are displayed every time, even to new recipients. This is only for Microsoft Outlook to combat the problem.

Prepare for disabled images

You’ve created a great template, you’re preparing to send to a list of permission-based subscribers, and you’ve taken the appropriate steps to get your email address into the recipients address book. But there will still be a number of people who intentionally block images, so you must prepare for that scenario.

1. Begin an email with HTML text or logical Alt text. You can decide what a reader sees in a preview pane. Some applications will allow you to preview the first few lines of text before an email is loaded.

2. Use Alt attributes. This is often missed or forgotten about and if your reader can’t see the image, all they’ll see is an empty white box.

3. Use captions for contextually important images. When Alt text is missing it’s important to add captions to images which are vital to the content of the email.

Avoid image based emails

Again, working within email marketing, this one may seem obvious, but image based emails are often thought to be an easy way to get your email to render irrespective of the recipients email client. But then again, your whole email could be blocked by a single preference.

Use the email marketer’s rule of thumb when it comes to text and images, stick to a 60:40 ratio in favour of text. Too many images will make your email get marked as spam.

In summary

Serious consideration should be given to image blocking and how you can work around it. It’s only normal that some people should disable them, but with the correct approach you can improve the experience for your subscribers.

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