mail/internal/mail/message.go
func NewMessage(settings ...MessageSetting) *Message {
	m := &Message{
		header:   make(header),
		charset:  "UTF-8",
		encoding: QuotedPrintable,
	}

	m.applySettings(settings)

	if m.encoding == Base64 {
		m.hEncoder = bEncoding
	} else {
		m.hEncoder = qEncoding
	}

	return m
}
func NewMessage(settings ...MessageSetting) *Message {
	m := &Message{
		header:   make(header),
		charset:  "UTF-8",
		encoding: QuotedPrintable,
	}

	m.applySettings(settings)

	if m.encoding == Base64 {
		m.hEncoder = bEncoding
	} else {
		m.hEncoder = qEncoding
	}

	return m
}
// NewMessage creates a new message. It uses UTF-8 and quoted-printable encoding
// by default.