I use Dr Brown 123 to package images for shipping and run it once on verticals, and once on horizontals. I send the same as our MLS wants then also Print size at 2700 pixel long edge and Web size at 1024 long edge I make the verticals come out with the same height as the horizontals, in terms of pixels, so the MLS show displays do NOT have the vertical of the smallest bathroom at twice the height of the gorgeous horizontal kitchen, etc. I deliver two sizes to all, three sizes to some.

While that size is overkill, when you naturally have that size, why take up additional hard drive space with a third group in the 3000px range. My full size (typically 7821X5217px 4.8MB if not cropped in composition processing) flat out won't upload to MLS for them to downsize.

While pixel is preferred measurement, size may matter as well as it combines with pixel dimensions. I deliver 2 sizes - 1500px (MLS and Web) and full size (suggest for brochures/printing) and label the file name on Lightroom export 'address' or 'address-1500px' to tell the difference with the sequential number remains the same between the two.

It also shows those Realtors not up with the times as they post postage stamps on current listings. My MLS had evolved over the years from 600, the 800 and now 1500 and those on the older standard when looking at historical listings show as postage stamps. Ask them - which would apply to all clients on same MLS - otherwise you have to call MLS to ask. Typically, when they upload a photo to MLS it states the recommended size, usually in both pixels and MB. May be able to avoid a call to MLS as many times the Realtor or their assistant may know.

Minium resolution for picture sizes