mail/internal/mail/writeto.go
func (m *Message) WriteTo(w io.Writer) (int64, error) {
	mw := &messageWriter{w: w}
	mw.writeMessage(m)
	return mw.n, mw.err
}
func (m *Message) WriteTo(w io.Writer) (int64, error) {
	mw := &messageWriter{w: w}
	mw.writeMessage(m)
	return mw.n, mw.err
}
func ( m * Message ) WriteTo ( w io . Writer ) ( int64 , error ) { mw := & messageWriter { w : w } mw . writeMessage ( m ) return mw . n , mw . err }
// WriteTo implements io.WriterTo. It dumps the whole message into w.
WriteTo implements io . WriterTo . It dumps the whole message into w .