NEVER open emails from an unknown source! The emails could be benign mass-mailings, mistakes, or viruses.

It isn't worth finding out which if you know they're not intended for you. If your mail program allows spam/bulk mail filtering, use that function. If not, delete the files immediately upon receipt.

Considering the fact that some of the emails have already been opened/read, you should do a thorough virus scan on all machines on your network as soon as possible.