Why is image to text ratio so important?
In email marketing, and since before HTML emails existed, spammers have tried to get people to buy their wares and infect computers. Then one day, spam filters learned to read and were able to block or divert to the junk folder any email mentioning common spammy words, like Viagra and replica watches etc.
Spammers in turn adapted by putting their content into images to avoid this. For a couple of years there was some back and forth, which is further explained in “Spammers vs the Spam Filter”, before images were blocked.
What does Spam Assassin look at?
Part of the bi-product of this was that content filters stopped liking image heavy emails. Any business server, which will use Spam Assassin, requires:
- A maximum of 40% image coverage
- A minimum 60% text coverage
- More than 3 images in the page – if any at all.
- Not all images touching
- At least 400 characters of text
…in the HTML version.
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.
Tips on how to make sure your emails are getting through
Add more text in the footer
The filter counts characters and allocates 12px to each letter
You can make then extra text smaller and more grey in the footer
Add a lot of alternate text
In this case you can add enough text to almost fill the image behind
This is not the full solution but can help a great deal
Where you have text in an image, make it actual text
This does mean that you have to have a solid colour background because back-images do not render in all inboxes