Why do improperly formatted emails come through, yet I can't block them?

I am getting a lot of spam emails with an oddly formatted address, and when I click to block them, I get a message that the address is improperly formatted and it does not let me block them.

For example, the sender's address will be something like, mailto:email address removed for privacy reasons mailto:admin@1234zxcv. Note the space between hotmail.com and admin, plus 2 "@" signs. In order to block it, I have to copy the part after the 2nd "@" sign and manually enter it in my blocked senders list ... which means I have to open the email (which, of course, Microsoft has told us we should not do).

If the address is improperly formatted, why in the world wouldn't that be a red flag for hotmail? Why would Microsoft even let an email like that come through?

Between the whose junk mail fiasco and this, I am beginning to wonder if ANYONE at Microsoft is paying attention.