add automatic greylisting

smtp/manager.go

@@ -40,6 +40,7 @@ type Manager struct {
 
 type matrixbot interface {
 	AllowAuth(string, string) bool
+	IsGreylisted(net.Addr) bool
 	IsBanned(net.Addr) bool
 	Ban(net.Addr)
 	GetMapping(string) (id.RoomID, bool)

smtp/server.go

@@ -59,6 +59,8 @@ func (m *mailServer) AnonymousLogin(state *smtp.ConnectionState) (smtp.Session,
 		getRoomID:    m.bot.GetMapping,
 		getFilters:   m.bot.GetIFOptions,
 		receiveEmail: m.ReceiveEmail,
+		ban:          m.bot.Ban,
+		greylisted:   m.bot.IsGreylisted,
 		log:          m.log,
 		domains:      m.domains,
 		addr:         state.RemoteAddr,

smtp/session.go

@@ -22,6 +22,7 @@ type incomingSession struct {
 	getRoomID    func(string) (id.RoomID, bool)
 	getFilters   func(id.RoomID) utils.IncomingFilteringOptions
 	receiveEmail func(context.Context, *utils.Email) error
+	greylisted   func(net.Addr) bool
 	ban          func(net.Addr)
 	domains      []string
 
@@ -76,6 +77,13 @@ func (s *incomingSession) Rcpt(to string) error {
 }
 
 func (s *incomingSession) Data(r io.Reader) error {
+	if s.greylisted(s.addr) {
+		return &smtp.SMTPError{
+			Code:         451,
+			EnhancedCode: smtp.EnhancedCode{4, 5, 1},
+			Message:      "You have been greylisted, try again a bit later.",
+		}
+	}
 	parser := enmime.NewParser()
 	eml, err := parser.ReadEnvelope(r)
 	if err != nil {