Using first body images instead of featured images
If your website is already set up with images in the body of your posts, or your theme doesn't use featured images specifically, or isn't displaying featured images the way you want, then using the first image in your post might be preferred for you as a workaround. We now include a simple checkbox to use the first image in the body of the post instead of the featured image. Simply check the "Use first image in body in RSS feed" box, and click Save.
Note: If you have both featured images set, and images in the post, checking this box will DISABLE the use of the featured image completely - it will be ignored. If converting a website over from not using featured images to using featured images, you should check this box while using your RSS feed and then add featured images to your most recent posts, and once done, you can uncheck this box and your site will be using featured images going forward.
If adding an image to the body of the post, then the Premium version (free trial or paid) adds a "Use first image in body" checkbox, and prepends it instead of the Featured Image.
If you switched from Featured Image to First Image in Body, and the Featured Image is still showing, it may be cached... try changing the RSS feed URL to "yourdomain.com/feed/?nocache" adding the "?nocache" to the end of it, and Mailchimp will pull it in fresh, otherwise it seems to cache the feed contents, including old images.