Disable CSS pre-processing
What’s CSS pre-processing?
By default, before emails leave Customer.io, we pre-process their CSS styles with Premailer to improve rendering. Before sending, Premailer:
- Converts CSS styles to inline attributes
- Converts relative paths to absolute paths
- Checks CSS properties against email client capabilities
You can find more details on Premailer’s website, as well as on the Github repository.
Why disable it?
If you’re using a custom email template which already has been pre-processed, running it through Premailer may cause some layout bugs. This most frequently happens with responsive email templates on mobile devices.
Disabling CSS pre-processing means that your CSS will stay exactly as specified in your template, avoiding these problems.
First, you’ll need to switch to the code editor in your email composer:
Then, you’ll see the option to disable CSS pre-processing:
Once that box is checked, your email will be sent as created in the code editor — no CSS pre-processing!
Because this is an advanced feature, disabling CSS pre-processing is only available in the code editor within the composer. Once you exit the code viewer and enter the Rich Text editor, pre-processing will be enabled again:
If you have any questions about this, please let us know!