What is the attachment called in your sent folder?

What is it called in the received email?

Hi Matt - Here`s the cod - DSCF2591.jpg 58.5KB

It is transferred in the email as jpg, on Picasa3 it plays the video perfectly

"jpg" is not recognised as being a movie file format. "jpg" is intended to contain a static photo. It's possible that whatever you're using to create or handle your movie is mis-labelling it. Some viewer/player programs do ignore the filename extension and look into the file where there is normally a string of characters indicating the file type. So in some cases, a movie file labelled "jpg" might be played.

Whether or not this is actually a movie file, Thunderbird is a mail client and not a movie player. It has limited capabilities for showing certain graphic file types (for example, jpg, gif, png).

58.5 KB is rather small for a movie. Possibly it's actually an animated gif, but ISTR that Thunderbird won't play these either.