They are spam emails and have included you in the BCC (blind copy) list.
If I were a spammer and had a valuable list of email addresses I wouldn't want to share them with other spammers, so I would choose one from the list and put the rest in the BCC box when composing my email.
This way you can't see who else the mail has gone to. It's like CC when composing an email. The only difference is that you can see who is in the CC list where you can't in the BCC list.
The only way to stop it would be to change email address or block who they are coming from (assuming it's the same address each time).
squarebear (what a nice nickname) is right, it's mostly likely spam emails. simply ignore them and delete everytime you get them. or you can use some email filter to deal with spam.
don't ever open spam emails and don't reply asking for unsubscribe, cos these ways you let the spammers know that your email address is in use and they can send more messages to you. that's my sad personal experience.
thanx all, i have put a block on the senders email addresses, so hopefully it will stop those ones sending them, but i have also noticed that alot of the senders are using loads of meaningless email names that obviously are rubbish such as [email protected] and so on.