Juergen Nieveler said:
Easy: In the HTML body are links to pictures that are loaded from a
spammers' webserver when you display the mail.
The link to the picture will contain a reference to the email address
used in the mail (sometimes coded, sometimes even in plain text) - so
the spammer just needs to check the logfile of his webserver to see
which of the millions of spams actually was viewed.
If you are using the current version of OE/O simply set it to view all email
in text mode only that way it can not even load in any graphics which some
spamers use to tag you. What they do is to send an html email which for all
intents and reasons is the same as a web page; but because of OE/O parsing
the html web page code you see the embedded graphics and such.
What a spammer(or anyone for that mater like a hacker or the likes) can
embed a very small graphic and then when you email parses the html and pulls
in the graphic to your computer the graphics being pulled from he spammers
computer lets them know that the person to whom they sent the spam is a
valid email address; because anyone that doesn't want email will not even
open such an email; but if you can't keep your self from clicking on every
email that comes into your email box from people you don't know, then I
suggest you do as I said earlier and set OE/O to view all email and news
groups as text only.
In case you don't know how to do this, go to Tools/options/read then
set it to "read all messages in plane text"
hth