builder.go
func (p MailBuilder) CC(name, addr string) MailBuilder {
	p.cc = append(p.cc, mail.Address{Name: name, Address: addr})
	return p
}
func (p MailBuilder) CC(name, addr string) MailBuilder {
	p.cc = append(p.cc, mail.Address{Name: name, Address: addr})
	return p
}
// CC returns a copy of MailBuilder with this name & address appended to the CC header.  name may be
// empty.