I produce html emails on a regular basis in my work.
Recently I've been baffled by the number of promotional emails I receive which use jpeg for images which would be far better served by a png or even a gif.
I've attached some examples from big name brands in the UK: ebay, Cotswolds (an outdoor clothing company) and The Guardian. They all include images with large areas of flat colour that would show less quality degredation/artefacting and have smaller file sizes if they had been saved as a png. Cotswolds even have their logo saved as a jpeg!
Is there a reason I'm not aware of that digitally savvy companies would use jpeg in these circumstances?
As far as I am aware, png is well supported in all major email clients these days. I understand using a jpeg for a photograph - but not a logo.
EDIT: With regards to file size, it is a misconception that jpeg is smaller.
For image like these (with large areas of flat colour), png will have a smaller file size. Jpeg was designed for photographs.
I saved an image of this style as a png, and a jpeg at the lowest file size possible via photoshop. The png is only 13.7kb. The jpeg is 20kb. The png is around 30% smaller.