As an ongoing headache, I regularly get emails from people with severely downsampled images so small that no text or details are readable. Screen shots, spreadsheets, etc. Which wastes everyone’s time.
The culprit is Apple Mail defaulting to a low-res size, typically “Small”.
Fortunately the fix is simple: make sure.
Of course if you really do want a downsized image, you can use the feature. But sending friends and family postage-stamp quality images is a bummer.