iPhone 5 iOS 7.0.6 sending text message to email address receives .txt attachment

I have searched high and low and there doesn't seem to be an answer to this question:

When sending a text message to an email address the person receives a .txt file with the text message inside the .txt file. How do we change this so the email is the actual text message instead of a .txt file?

This seems so simple, but the answer can't be found anywhere. I hope someone can help!

I have AT&T if that matters to anyone. Also, I'm not sure when this .txt file thing changed, but I used to be able to send text messages to email addresses with no problem.