Why do I receive messages addressed to other people?
Incorrect delivery of a message is extremely unlikely. There are two reasons you may receive messages not specifically addressed to you:
Your email address is in the "To:" or "Cc:" field, but the sender is addressing you as a different person. This is most likely a case of mistaken identity, since it's not possible for two people to unknowingly share the same Yahoo! ID/email address. One incorrect character in an email address can cause the message to be sent to the wrong account.
If you can't find your address in the "To:" or "Cc:" field, it has most likely been included in the "Bcc:" ("Blind Carbon Copy") field of the message. It will look as if you've received someone else's message since your address won't appear anywhere in the header.
If you've received a message apparently addressed to someone else, you may want to contact the sender for further information or to alert them of the mistake.
Additionally, if you see a only a person's name in the "To:" field, it may be that the sender has you included in a list of contacts. The name appearing would be the name given to that list and appears to maintain the anonymity of the other recipients on the list.
Hope that helps.