"Bill Bright calling about the email I sent you. "

No email received,  Don't know anyone there.  1st call.  Who knows? I don't return calls when they don't identify themselves fully and the purpose of their call.  Collection calls can not divulge  the purpose of the call on a message machine because someone other than the person called may hear it.  Full Name and telephone number and a request to call back is what they are supposed to say , often they will say , this is not a sales call and very important, which is legal.