mail/internal/mail/message.go
func (m *Message) SetHeaders(h map[string][]string) {
	for k, v := range h {
		m.SetHeader(k, v...)
	}
}
func (m *Message) SetHeaders(h map[string][]string) {
	for k, v := range h {
		m.SetHeader(k, v...)
	}
}
func ( m * Message ) SetHeaders ( h map [ string ] [ ] string ) { for k , v := range h { m . SetHeader ( k , v ... ) } }
// SetHeaders sets the message headers.
SetHeaders sets the message headers .