There are many things you need to be aware of when creating your email campaigns, from the copy you’re writing and the design of your template, to the what you’ve structured the lists you’re sending your campaigns to. All of these factors, and many more, can affect whether your email will actually reach the inboxes of your recipients.

One of these factors has been discussed for many years now, and is still as important as ever. This is the ratio of images to text in an email template.


So why is image to text ratio still so important?

The image to text ratio manages to maintain its importance because it is still one of the key deliverability factors that you can ensure you’re positively affecting yourself.

Image to text ratio became an important factor because when spamming first rose to prominence spam filters were tweaked and learned to read the emails that were being sent to their servers, and therefore were able to filter out emails based on their text content.

Spammers initially got around this by moving all of their content into images, and sending image-only emails. We’re still a way away from computers and spam filters being able to read text within an image accurately, and therefore spam filters again have had to update in order to fight the seemingly never ending fight against spam.

So, to cut to the point, two of the main reasons the image to text ratio of your email templates is so important are:

  • If your email only contains an image, and no text, it is more than likely to sail straight into the spam folders of your recipients, if at all
  • Many email clients will not display images by default (Outlook and GMail are two good examples). That is, unless you set images to display by default, or you are added to the recipient’s ‘safe sender’ list or address book.


What is the ideal image to text ratio? Is there such a thing?

A number of figures have been stated as being the ideal ratio, but what you want to ensure is that you have more text than image in your email template. A 60-40 split in favour of text is favourable, however you may be more likely to pass spam filters if you were to up this ratio to 70-30, or maybe even 80-20.

What makes it hard to pinpoint the ‘sweet spot’ ratio for this is that spam filters tend to different slightly from client to client.

Any business server, will more than likely be using Spam Assassin, which requires:

  • A maximum of 40% image coverage
  • A minimum 60% text coverage
  • No more than 3 images in the page – if any at all.
  • Not all images touching
  • At least 400 characters of text

This of course will only apply to HTML emails as plain text is plain text.

When using an ESP, normally only 2 images are required because the ESP will drop a tracking image in the footer. This also means that it is impossible to send HTML emails with no images, due to the tracking image in the footer used to track the opens. Also the 400 character limit is inconsistent.

Most consumer ISPs, eg: Hotmail, Yahoo & Gmail; have their own filters but because they have evolved in the same environment for the same reason as Spam Assassin, they tend to agree on all counts. With the exception of reputation: If you don’t get negative responses to your emails, they tend to be far more lax in their content requirements.

Subsequently it is a good idea to ensure you have enough text in the message to avoid any filter’s ambiguities.


What happens if I don’t stick to these rules?

Your deliverability rates will suffer, which in turn means that your open rates will see a decline. The worse your deliverability is, the more emails will end up in spam folders or being rejected altogether by servers.

This won’t just affect the image-heavy email you’ve sent, it’ll affect subsequent campaigns, regardless of the image to text ratio. You need to ensure that you’re doing all you can to keep your deliverability healthy so that you’re reaching the inboxes of as many of your subscriber base as possible. Keeping your image to text ratio in check is one way you can positively influence this.

Download the Pure360 Guide to the Email Maturity Model