If two people have similar addresses and a sender mistypes the address in
such a way that it matches the other address and then sends the mail, then
naturally the incorrect mailbox will receive the message.  It's no different
that a misdialed phone number.  If someone can make a mistake by leaving out
a period in the address, then obviously someone else can make a mistake and
add one where none should be.  However, the other person isn't "reading your
mail".  S/he may get the occasional misaddresses message, but s/he has no
access to the messages you've correctly received.