Why does blocking a spam email end up blocking my own address?

The spammer is "spoofing" the "From:" address. By that I mean that they're not using their real address, but making one up. Or using some other random address as the "From:" address. Or yours.

In fact, they often get creative: you'll often see some other name, but the email address is completely different and unrelated. So often you'll see a unfamiliar name in the "From:" line, but if you look at the email address that's associated with that name, you'll see it's completely different, and possibly even your own:

From: Leo A. Notenboom <someoneelse@example.com>

It looks like someone, but has the email address of someone else. Just another way to hide what's really happening in spam.

So why do spammers go through all these steps? Two reasons: first, they naturally want to hide where they're sending from specifically so you can't block them. Second, by setting the "From" address to be yours, if the mail bounces you'll still get it as the mail system attempts return the mail to the sender identified by the "From:" address.

How did they get your email address? There are so many ways. Two of the biggest ways are harvesting them from web pages or forums where you've provided your email address, and viruses that steal address books.

What can you do about it?

Nothing.

If spammers are constructing "From:" addresses with your email address there's literally nothing you can do. You wouldn't want to block it because as you've seen, you'd be blocking yourself.

The best you can do is hope that your other spam-fighting techniques such as content filtering catch the spam before you see it. Beyond that, I find the delete key exceptionally valuable.