No, most SPAM nowadays is sent as HTML, containing an image or two - simple statistical tracking can be done by looking at the http servers referral logs.

More advanced SPAM software, such as that used by large corporations for 'legitimate' SPAM include such niceties as a zero-sized transparent gif with a unique per-email name - the http server matches the request for the gif to the email address...hence validating the email address.
_________________________
Mk2a 60GB Blue. Serial 030102962 sig.mp3: File Format not Valid.