'Emailing a jpeg' oddness

I just sent a jpeg to someone via email at a requested size, dpi etc as a jpeg. I use Apple's Mail as my email client.

They replied that it had arrived as "as a bit map".

I forwarded it to myself as a test and it arrived as a jpeg. Just to force the matter I zipped it before sending it to them again.

Any ideas what was going on here? I've no idea what platform etc the recipient is using.

Depends on what email client and OS they're using and how exactly they tried to save the attachment.

E.g., if they're using web-based email with Internet Explorer, then if they opened the JPEG within IE and then right-clicked to Save As, IE allows the user to change the file type to BMP and save it as a bitmap file. I.e. PEBCAK...

jon