You might have the experience of receiving a junk email that appears to be for someone else. How come an email not addressed to you arrive at your mailbox? Is it an error on the email system?
No, fortunately. Email is a very reliable technology and delivery to the wrong email address will not happen. What hide your address from the recipients' list is the BCC (Blind-Carbon-Copy) feature being exploited by spammers.
There are three recipients' lists one can type email addresses into when sending an email: TO, CC and BCC. Both TO and CC appears on the email header, but by email convension, BCC will be stripped from all recipients' copies.
The BCC feature is used when you want to copy the email to someone else but do not want other recipients to know. For example, replying a customer's enquiry and BCC to your boss. (One may discuss the ethical issues in using BCC but it's been around in the paper mail ear, long before computers were invented.)
Spammers exploit BCC to evade detection and to include as many recipients' address as possible (as some email servers have a limit on the TO and CC lists). On the other hand, BCC is useful for mailing list senders as they can include the list names in BCC so that members will not see each other's email addresses. It is a two-edge sword.
Next time when you receive an email without your email address on the TO or CC list, don't worry. You are not receiving other people's junk email. Simply delete them as you do other spam.