This is for Gmail users. I use this to get a little more proof against spam. Turn on “Ask before displaying images”.
With it turned on, when you get an email from someone new, Gmail will ask if you want to view images from them. I find this to be a nice, little reminder to be alert against spam. For instance, when I get an email from my bank but the images aren’t being displayed, it’s probably because it’s not actually from my bank!
This also might decrease the spam you get in the future since spammers make a note of when people look at images in their emails as a sign that they are active email accounts.