When you say "Photoshop format" do you mean Psd files? and secondly, are the layers flattened?
Its important to flatten/merge the layers otherwise the resulting image file would be huge -? causing the crashes.
Also, unless the recipient of your mail has Photoshop then they will not be able to open the file anyway.
To convert in Photoshop, go via "save as" then choose a more common file-type - JPEG for example but do keep an eye on the file size regardless of the format (75 pixels is more than adequate for desktop viewing).