All HubSpot drag-and-drop templates are responsive by default. This means the content adjusts to fit the screen it's viewed on. HubSpot also adds a max-width to images in the content editor, so you don't have to worry about editing the source code to add max-widths.
In most cases, download speeds on mobile devices are slower than on desktop. Use smaller image files to decrease your email load time. HubSpot automatically resizes your images that include a width attribute in an <img> tag. Services such as FastStone Photo Resizer and JPEGmini can also reduce file size by as much as 80% without reducing the quality of your image.
Increase the size of links and CTA buttons
Make sure your content is large enough to be read clearly on a mobile device. To ensure your subscribers can see and click on your content clearly, make sure any text links and CTA buttons are taller and wider than 57x57 pixels.
Preview your email on mobile devices
Before sending your email to your lists, you can preview what it will look like across different clients and devices.
Within the HubSpot email editor, click the Checkmark in the left sidebar pane to test your email in other email clients. Select the desired email clients in the Mobilesection and click Test my email now to generate previews of what your email will look like in those clients.
You can also use the device preview tool by clicking the eyeiconview on the left sidebar pane to quickly see what your email will look like on a desktop, tablet, or mobile phone.