diff --git a/conn.go b/conn.go
index ec9f686..2c3605e 100644
--- a/conn.go
+++ b/conn.go
@@ -276,6 +276,9 @@ func (c *Conn) handleGreet(enhanced bool, arg string) {
 	if c.server.EnableDSN {
 		caps = append(caps, "DSN")
 	}
+	if c.server.EnableXOORG {
+		caps = append(caps, "XOORG")
+	}
 	if c.server.MaxMessageBytes > 0 {
 		caps = append(caps, fmt.Sprintf("SIZE %v", c.server.MaxMessageBytes))
 	} else {
@@ -339,6 +342,12 @@ func (c *Conn) handleMail(arg string) {
 			}
 
 			opts.Size = int64(size)
+		case "XOORG":
+			if !c.server.EnableXOORG {
+				c.writeResponse(504, EnhancedCode{5, 5, 4}, "EnableXOORG is not implemented")
+				return
+			}
+			opts.XOORG = value
 		case "SMTPUTF8":
 			if !c.server.EnableSMTPUTF8 {
 				c.writeResponse(504, EnhancedCode{5, 5, 4}, "SMTPUTF8 is not implemented")
diff --git a/server.go b/server.go
index 7c23a31..d1ebbae 100644
--- a/server.go
+++ b/server.go
@@ -57,6 +57,10 @@ type Server struct {
 	// Should be used only if backend supports it.
 	EnableDSN bool
 
+	// Advertise XOORG capability.
+	// Should be used only if backend supports it.
+	EnableXOORG bool
+
 	// The server backend.
 	Backend Backend
 
diff --git a/server_test.go b/server_test.go
index 206d336..31600bc 100644
--- a/server_test.go
+++ b/server_test.go
@@ -1514,3 +1514,47 @@ func TestServerDSNwithSMTPUTF8(t *testing.T) {
 		t.Fatal("Invalid ORCPT address:", val)
 	}
 }
+
+func TestServerXOORG(t *testing.T) {
+	be, s, c, scanner, caps := testServerEhlo(t,
+		func(s *smtp.Server) {
+			s.EnableXOORG = true
+		})
+	defer s.Close()
+	defer c.Close()
+
+	for _, cap := range []string{"XOORG"} {
+		if _, ok := caps[cap]; !ok {
+			t.Fatal("Missing capability:", cap)
+		}
+	}
+
+	io.WriteString(c, "MAIL FROM:<e=mc2@example.com> XOORG=test.com\r\n")
+	scanner.Scan()
+	if !strings.HasPrefix(scanner.Text(), "250 ") {
+		t.Fatal("Invalid MAIL response:", scanner.Text())
+	}
+
+	io.WriteString(c, "RCPT TO:<e=mc2@example.com>\r\n")
+	scanner.Scan()
+	if !strings.HasPrefix(scanner.Text(), "250 ") {
+		t.Fatal("Invalid RCPT response:", scanner.Text())
+	}
+
+	// go on as usual
+	io.WriteString(c, "DATA\r\n")
+	scanner.Scan()
+	io.WriteString(c, "Hey <3\r\n")
+	io.WriteString(c, ".\r\n")
+	scanner.Scan()
+	if !strings.HasPrefix(scanner.Text(), "250 ") {
+		t.Fatal("Invalid DATA response:", scanner.Text())
+	}
+	if len(be.messages) != 0 || len(be.anonmsgs) != 1 {
+		t.Fatal("Invalid number of sent messages:", be.messages, be.anonmsgs)
+	}
+
+	if val := be.anonmsgs[0].Opts.XOORG; val != "test.com" {
+		t.Fatal("Invalid XOORG parameter value:", val)
+	}
+}
diff --git a/smtp.go b/smtp.go
index 9563b11..ab0c105 100644
--- a/smtp.go
+++ b/smtp.go
@@ -56,6 +56,9 @@ type MailOptions struct {
 	// Envelope identifier set by the client.
 	EnvelopeID string
 
+	// Accepted Domain from Exchange Online, e.g. from OutgoingConnector
+	XOORG string
+
 	// The authorization identity asserted by the message sender in decoded
 	// form with angle brackets stripped.
 	//