I agree it is annoying that an e-mail send to WHD always creates a new client if he/she is not already in the database. In our case it is not only for vendors, but we have "generic e-mail accounts", for example email@example.com. Almost all departments (over 100x) have generic e-mail accounts which the departmental secretary use.
So not only the users, students (which obviously are in the database) but generic e-mail accounts, vendors or users with private e-mail accounts will generate new clients in WHD. So for one user (firstname.lastname@example.org) we could have three to four different clients:
It is possible to restrict WHD to accept incoming e-mails only from specific domains. That would rule out, for example @gmail.com accounts, but for various reasons we can't do this.
Maybe somebody had a good idea of how to streamline the incoming e-mails.