mail/internal/mail/message.go
func (m *Message) SetAddressHeader(field, address, name string) {
	m.header[field] = []string{m.FormatAddress(address, name)}
}
func (m *Message) SetAddressHeader(field, address, name string) {
	m.header[field] = []string{m.FormatAddress(address, name)}
}
// SetAddressHeader sets an address to the given header field.