Oh, so all you want to do is have another e-mail tool be your default. Can you tell me what type of link you are referring to in "It's the clicking on a link to send mail to a vendor that causes Mail to open over my normal email platform." That sounds like some type of link in a browser, and you click on a link in a browser to send or receive an e-mail" Is that correct? If that is correct that is a very simple fix:
In the Mail App - Preference - General tab - Default E-mail reader and then select the e-mail tool want.
You were less than descriptive in what you wanted to achieve so that is why you got the original answer you got. Perhaps going forward you would benefit by looking over Writing an effective Apple Support Communities Question