Hello Firemission and welcome to the BC HijackThis forum. Unless you know the sender of the email and know that they have sent you an email with an attachment, I would not recommend attempting to open it. Emails can be sent from known recipients whose PC's have been compromised by any number of computer infections running wild on the internet today.
That said, you should contact the sender to first confirm that they actually sent the email and then to find out what the attachment is. Even if it is a valid email with a valid attachment, you will need the program which created the attachment to open it up.
The HijackThis forum deals exclusively with virus and malware issues. For assistance with email questions I would suggest posting in the Web Browsing/Email and Other Internet Applications
forum. The techs there can assist with issues related to those applications.