Spam Mail. Does anyone know how to resolve my Email problem?

I have an E-mail address as a contact the contact person is a friend of mine but what is happening their email address is being mimicked. I'll give you an example: Say my friends name is Jackie Jameson. Her email is "JacJ@gmail.com" so when she sends mail to me her address should be: Jackie Jameson However what has been happening is the mail I have been receiving has Jacay Jameson therefore every part of her E-mail address except her last name in the first part. I want to place a block to stop all mail from being sent from this particular place as this isn't the first email I have received. However, I don't want to prevent my friend from being able to send mail over to me either.