But then you also have to download something in the e-mail first.
But yes, an image could probably do it or something. I'm not sure, but I guess that's why images are automatically replaced by grey squares or something similar in most e-mail systems.
But, since there are security systems in the e-mail systems, you shouldn't worry too much, in this case at least. Also, e-mails containing viruses are often slightly obvious since you normally wouldn't expect to get an e-mail from the address with the subject.
You could also try to get an alternative e-mail address, so if you have for example 1111@e-mail.com, you could register 2222@e-mail.com, and make 2222@e-mail.com automatically send the e-mails it receives to 1111@e-mail.com. I do that, and then I register the places I'm concerned about with my alternative e-mail address. If spamming should one day become a problem, then I can just stop my alternative e-mail address from sending to my main.