Your shop's logo now shows in every email app

A logo could come out blank or oversized depending on which email app the customer opened it in. Emails now tell the app exactly how big to draw it, so it looks the same everywhere.

Outlook — it ignores the styling other apps use, so it was falling back to the logo's full original size. Emails now carry the exact dimensions, which Outlook does read.
A very large logo no longer breaks — one shop's file was 9000 pixels across, which no email app will open, so it showed as a broken image. Logos are resized when you upload them, and the old one has been fixed.
Nothing to do on your end — your logo is unchanged, and the original file you uploaded is untouched.