mail/internal/mail/message.go
func (m *Message) EmbedReader(name string, r io.Reader, settings ...FileSetting) {
	m.embedded = m.appendFile(m.embedded, fileFromReader(name, r), settings)
}
func (m *Message) EmbedReader(name string, r io.Reader, settings ...FileSetting) {
	m.embedded = m.appendFile(m.embedded, fileFromReader(name, r), settings)
}
// EmbedReader embeds the images to the email.