mail/internal/mail/message.go
func (m *Message) AttachReader(name string, r io.Reader, settings ...FileSetting) {
	m.attachments = m.appendFile(m.attachments, fileFromReader(name, r), settings)
}
func (m *Message) AttachReader(name string, r io.Reader, settings ...FileSetting) {
	m.attachments = m.appendFile(m.attachments, fileFromReader(name, r), settings)
}
// AttachReader attaches a file using an io.Reader