What Pharma Marketers Should Know about Email Service Provider (ESP) Image Blocking

Collecting accurate data from email is essential to pharma marketers as it provides valuable insight into the effectiveness of both the promotional content and email as a marketing channel. As pharmaceutical companies invest money to deliver promotional messages to target audiences, they want to ensure their emails are being opened and read, yet the obstacle of ESP (email service provider) blocking affects the possibility of messages reaching the physicians that brands want to target.

The biggest motivation behind ESP blocking is the need to preserve privacy and give users control over their email. Image blocking is a growing problem for marketers since tracking pixels (which capture the data) are images, and if images are blocked, the reporting of accurate email sends, open rates, clicks, and engagement is becoming increasingly compromised.


Currently, there are no standard settings for image blocking across email providers. Email clients like Outlook, Gmail, Yahoo, and others have their own default settings or filters when it comes to downloading images. Other factors, such as device or browser, may cause the email to open in text mode or may have extensions that disable the tracking pixels. These settings are typically enabled to lower the risk of viruses.

Various email clients handle images in different ways. For example, Outlook does not block images by default, but rather blocks what is considered a suspicious-looking sender; however, images are automatically blocked on mobile browsers. Alternatively, Yahoo blocks all images, background colors, and links by default, and only the text version is available when an email is initially opened.


Sending promotional messages via email is an effective way of reaching target physicians with brand information. Based on the CMI/Compas Media Vitals™ physician survey, 52% of HCPs open and skim emails from pharmaceutical manufacturers, and 59% do the same from medically relevant publishers. The number of users that opened and viewed the content combined with those users that also clicked through to the landing page is referred to as the click-to-open rate. The click-to-open rate is the primary measure of email performance, but should be viewed as a directional metric. The open rate by itself does not communicate the full picture of whether or not the content is meaningful and engaging to the target audience. There is an imperfect nature to emails, and marketers need to look at the engagement data alongside the open rates; however, image blocking is preventing a complete and transparent view into the email performance data.


It is difficult to combat image blocking with many email clients automatically blocking images or due to user-adjusted settings. Nevertheless, there are several strategies that can be employed.

Alternative text (shortened as ALT text) is the most common technique to counter image blocking. Adding ALT texts to emails would allow the physician to see a text explaining the blocked image instead of a blank box. In order to make the ALT text more appealing and compelling for the physician to disable the image blocking, an inline Cascading Style Sheet (CSS) can be added to change the color, style, font, and size.

Bulletproof buttons work by protecting the call-to-action (CTA) buttons, which are designed as images and blocked when images are disabled. The CTA buttons redirect physicians to a variety of landing pages, while bulletproof buttons are live text that replace the CTA buttons once images are disabled.

Always use a mix of imagery and text. Avoid an all-image-based design in favor of preserving balance between images and text. When a proper balance between imagery and live text is implemented, the physicians’ connection to the content is maintained whether the images are blocked or not. This technique can prevent filters from registering the email as spam.

Background colors involve the addition of selected colors behind the images that remain if the images are blocked. The colorful background improves the visual perception to the physician, hopefully compelling them to take action.

Mosaics and pixel art utilizes the background colors coupled with images to create appealing and striking texts that captivate the user in the absence of images.

Creative agencies can combine two or more techniques to create an email that would encourage the physician to open and unblock the images.


With so many email clients preventing images from downloading, and some physicians choosing those settings on their own, image blocking is unavoidable. It’s up to creative agencies and email partners to make the content stand out, regardless of whether images are enabled or not. Luckily, there are creative methods that agencies may use to help facilitate the opening of emails. However, it is important to realize that not all opens will be captured, and HCPs may be exposed to a brand’s content that were simply not recorded or tracked due to image blocking. Clients using email to deliver promotional messages to target audiences need to take into consideration that the collected data on the emails may not be 100% accurate.