Your guide to image optimisation in email

How long do you like to wait for an image to download? I’m guessing no time at all. If you’re anything like me you expect things to load and be available in a flash, but let’s take a closer look at what the data says about how long it takes to load 1MB in an email:

2G Edge (0.1 Mbit/s) 80 seconds
3G Basic (0.1 Mbit/s) 80 seconds
3G - H (1.5 Mbit/s) 5.3 seconds
3G - HSPA+ (4 Mbit/s) 2 seconds
3G - DC-HSPA+ (8 Mbit/s) 1 second
4G - LTE (15 Mbit/s) 0.53 seconds

Why is it important to optimise your images?

We all know that having a good image to text ratio is crucial when it comes to your email campaigns - but just like you place your text and spend time to ensure your message comes across in the way you intended, your images are just as important.

Images in your campaigns are able to enhance the overall email experience you give your subscribers and can be incredibly flexible. Optimising your images can give you a competitive edge over your competitors. If you’ve been nervous about adding visual elements to your email campaigns, we’re going to show you how you can overcome your fears.

Size guidelines

We always recommend that people keep the content of their emails within a 600px width (our platform even shows this when you are busy setting up your campaigns).

Email width settings!

This means, depending on the design layout you choose for your campaigns, you’d want to adjust your images accordingly.

If you need to use full width background images for your email campaigns, we’d recommend that you use repeatable patterns as your image will show up differently in different email clients. We recommend this as there’s no “one size fits all” rule in this area. Repeatable patterns however, might look better than a single image background.

If you use a background image, you should ALWAYS add a similar background colour, just to be safe.

Background image settings!

Image formats

JPEG, PNG, SVG or GIF? Feeling confused as to what image format you should use? Let’s take a closer look at each different image format to help you make an informed choice.

JPEG (Joint Photographics Expert Group)

Sometimes also referred to as JPG, is as the name suggests a format that is widely used for photography. When JPEGs are not compressed and in their ‘raw’ format, they can be high quality graphics that can lose their quality if manipulated or saved incorrectly.

JPGs do not accommodate transparent backgrounds. If you for example export a file via Adobe Photoshop to JPG, a white background will automatically be applied.

PNG (Portable Network Graphic)

PNGs are ideal for website graphics and (spoiler alert) allow you to have images with transparent backgrounds. If you have a logo, illustration or graphic where you want to get and keep the maximum capacity, PNGs are the way to go. Another interesting aspect of using PNG files is that they are lossless. This essentially means that when you save the exact same file as a JPEG as a PNG, the PNG version would have a larger file size. You may be thinking this is a bad thing if you can just use a JPEG but the PNG will retain the quality of your graphic which would make the larger file size worth it.

SVG (Scalable Vector Graphics)

SVG’s are a file format that helps you scale images to any size without actually losing any quality. There are no other file types that look as great as SVGs. SVG’s are actually coded and defined by a series of math equations that define shapes, colours and sizes. SVGs are best suited for logos, icons or simple graphics.

Some downsides to using SVGs is that it’s a bit of a learning curve to create them. You can only create them in programmes like Illustrator, Sketch or other vector-based programmes. Besides that there are also a lot of marketing channels that do not support SVG files. A common workaround for this is to copy SVG code in a code block, but again you’d need to have the skills to do that.

Image file size (or file weight)

Large images will take longer to load as seen in the table at the beginning of this article. We recommend that you keep your image file weight to 1MB max (where possible). If you can even have a lighter image than 1MB, that will be much better. Your goal ultimately is to give your subscribers the best possible email campaign experience and no one likes to wait for images to load. A large percentage of your audience will also most likely read your email on their mobile devices and as such you want to be accommodating to their data usage.


Did you know that images you see are specifically saved for web or print? There are two colour modes for your images, namely RGB and CMYK. RGB is the web based colour setting that is used for all images assets on the web and CMYK is used for print based assets. You want to ensure that you use the right colour settings when you are creating assets for your emails.

Alt text is important

Now that you have more information about how you can optimise your images, it’s important for you to also optimise and account for instances where your subscriber’s might not see your images. Cue, alt text. This nifty email marketing addition gives you the ability to add text to your images that will only be displayed when the image cannot load for whatever reason.

Alt text can help your subscriber to understand what you want to communicate even when they can’t see the images that support your message.

Keep the following in mind when you are adding your alt text:

  • Keep your alt text short and sweet (no more than two lines at most)
  • Punctuation is important
  • If your image contains text, add the exact text as your alt text
  • If an image is just decorative, you can make your alt text “decorative image”
  • Don’t use quotation marks in your alt text - it could break your email

Sourcing images

If you don’t really have time, budget or energy to create your own unique images for your business, you can use stock photography. Stock photography gives you a wide variety of images to choose from and can be completely free too.

We’ve rounded up Free Stock Photography Resources that you can look at to see which suit your business best. We also have a built-in Pexels integration that makes it easier than ever to add free stock images to your campaigns.


  • To summarise, these are the main things to keep in mind when you are creating email assets:
  • Customise your assets to fill your email structures and content blocks by sizing them correctly
  • See how you can compress your images so that they aren’t more than 1MB in file weight
  • Pick an image format that suits the asset you are using
  • Focus on adding useful and descriptive alt text to all your images in your email campaigns
  • Source images in line with your unique brand, if you can create your own images that would be first prize, but if you can’t then research some stock photography options

Have any questions about images and using them in your campaigns? Ask us in the comment section below.


Contact us
for help

Fill out the form and we will get back to you.

Join Our

Ready to enhance your email marketing campaigns?
Sign up to our weekly email newsletter for email marketing news, tips and tricks.