Mac G5 Os X - Mail


Allow I have a Mac G5 running OS X. While using the Mail software, the computer changed its smtp on its own. I was trying to send out an e-mail and error message came back telling me that the server could not be connected. Upon further review, I realized that the smtp that was selected was not the correct one. This changed in the computer on its own with out me doing anything. Why is this occurring?

Thank you