Custom image size

If you want to use your own image size instead of small, medium, or the custom image size registered by the plugin, you can register your own image size and add it to the options available to the plugin using the send_images_rss_thumbnail_size_list filter (ref). The settings page is set up to only show those three sizes by default, but you can use any size you have registered.

Note: if you have not disabled the image size registered by the plugin, I would just use that (you can adjust it on the settings page). Images uploaded before the plugin was activated will not have copies at the new/smaller image size, so if you are seeing older images at large sizes, that may be why (ref).

This is what I have at the moment https://prntscr.com/pxgszq. How do I know the size generated by the plugin? Or is it the 1120 0ne? I regenerated thumbnails and it showed 560×293 but I cannot see that in the settings. 1120 is too big a height for an RSS image.

The plugin’s image size is the one called mailchimp. The dimensions are general, not exact–if you upload a horizontal image, for example, it might be 560px wide, but only 293px high. Most images will not be that tall, but the 560 is generally the width of an email (you can change that number with the setting above as well). Alternatively, if you upload something like an infographic which is really tall, it will be 1120 tall at the most, but may be narrower than 560. Hope that helps clarify–

My images are generally 1200×628. O I am assuming the height is auto for the plugin? And for the filter you shared above, any way to call it from my functions.php rather than editing the plugin itself?

Yes, the height is automatically handled based on the width, unless it’s a vertical/portrait orientation photo. If that’s your typical image size, the mailchimp size image will be 560×293, as you mentioned in your reply above.

It seems to work after I regenerated the thumbnails. Not sure why it shows the height as 1120 in the dropdown.