diff --git a/pkg/message/manager.go b/pkg/message/manager.go
index 0224035..1ef8089 100644
--- a/pkg/message/manager.go
+++ b/pkg/message/manager.go
@@ -112,7 +112,7 @@ func (s *StoreManager) Deliver(
 	for _, mb := range inbound.Mailboxes {
 		// Append recipient and timestamp to generated Received header.
 		recvd := fmt.Sprintf("%s  for <%s>; %s\r\n", recvdHeader, mb, tstamp)
-
+		returnPath := fmt.Sprintf("Return-Path: <%s>\r\n", from.Address.Address)
 		// Deliver message.
 		logger.Debug().Str("mailbox", mb).Msg("Delivering message")
 		delivery := &Delivery{
@@ -124,7 +124,7 @@ func (s *StoreManager) Deliver(
 				Subject: inbound.Subject,
 				Size:    inbound.Size,
 			},
-			Reader: io.MultiReader(strings.NewReader(recvd), bytes.NewReader(source)),
+			Reader: io.MultiReader(strings.NewReader(returnPath), strings.NewReader(recvd), bytes.NewReader(source)),
 		}
 		id, err := s.Store.AddMessage(delivery)
 		if err != nil {
diff --git a/pkg/message/manager_test.go b/pkg/message/manager_test.go
index cf96b59..99d28b2 100644
--- a/pkg/message/manager_test.go
+++ b/pkg/message/manager_test.go
@@ -501,6 +501,38 @@ func TestMailboxForAddress(t *testing.T) {
 	assert.Equal(t, addr, got, "FullNaming mode should return a full address for mailbox")
 }
 
+func TestReturnPath(t *testing.T) {
+	sm, _ := testStoreManager()
+
+	recvdHeader := "Received: xyz\n"
+	msgSource := `From: from@example.com
+To: u1@example.com
+Subject: return path
+
+test email`
+
+	// Deliver message.
+	origin, _ := sm.AddrPolicy.ParseOrigin("821from@example.com")
+	recipient, _ := sm.AddrPolicy.NewRecipient("u1@example.com")
+	err := sm.Deliver(origin, []*policy.Recipient{recipient}, recvdHeader, []byte(msgSource))
+	require.NoError(t, err)
+
+	// Find message ID.
+	msgs, err := sm.GetMetadata("u1@example.com")
+	require.NoError(t, err, "Failed to read mailbox")
+	require.Len(t, msgs, 1, "Unexpected mailbox len")
+	id := msgs[0].ID
+
+	// Read back and verify source.
+	r, err := sm.SourceReader("u1@example.com", id)
+	require.NoError(t, err, "SourceReader must succeed")
+	gotBytes, err := io.ReadAll(r)
+	require.NoError(t, err, "Failed to read source")
+
+	got := string(gotBytes)
+	assert.Contains(t, got, "Return-Path: <821from@example.com>\r\n", "Source should contain return-path")
+}
+
 // Returns an empty StoreManager and extension Host pair, configured for testing.
 func testStoreManager() (*message.StoreManager, *extension.Host) {
 	extHost := extension.NewHost()
diff --git a/pkg/test/testdata/basic.golden b/pkg/test/testdata/basic.golden
index 31035dc..e01ad2e 100644
--- a/pkg/test/testdata/basic.golden
+++ b/pkg/test/testdata/basic.golden
@@ -2,7 +2,7 @@ Mailbox: recipient
 From: <fromuser@inbucket.org>
 To: [<recipient@inbucket.org>]
 Subject: basic subject
-Size: 204
+Size: 242
 
 BODY TEXT:
 Basic message.
diff --git a/pkg/test/testdata/encodedheader.golden b/pkg/test/testdata/encodedheader.golden
index cd2d5d8..1d756e1 100644
--- a/pkg/test/testdata/encodedheader.golden
+++ b/pkg/test/testdata/encodedheader.golden
@@ -2,7 +2,7 @@ Mailbox: recipient
 From: X-äéß Y-äéß <fromuser@inbucket.org>
 To: [Test of ȇɲʢȯȡɪɴʛ <recipient@inbucket.org>]
 Subject: Test of ȇɲʢȯȡɪɴʛ
-Size: 338
+Size: 376
 
 BODY TEXT:
 Basic message.
diff --git a/pkg/test/testdata/fullname.golden b/pkg/test/testdata/fullname.golden
index 31bb3d2..82bd0dc 100644
--- a/pkg/test/testdata/fullname.golden
+++ b/pkg/test/testdata/fullname.golden
@@ -2,7 +2,7 @@ Mailbox: recipient
 From: From User <fromuser@inbucket.org>
 To: [Rec I. Pient <recipient@inbucket.org>]
 Subject: basic subject
-Size: 233
+Size: 271
 
 BODY TEXT:
 Basic message.
diff --git a/pkg/test/testdata/no-to-ipv4.golden b/pkg/test/testdata/no-to-ipv4.golden
index af7a9e5..ff08189 100644
--- a/pkg/test/testdata/no-to-ipv4.golden
+++ b/pkg/test/testdata/no-to-ipv4.golden
@@ -2,7 +2,7 @@ Mailbox: ip4recipient
 From: <fromuser@inbucket.org>
 To: [<ip4recipient@[192.168.123.123]>]
 Subject: basic subject
-Size: 180
+Size: 218
 
 BODY TEXT:
 No-To message.
diff --git a/pkg/test/testdata/no-to-ipv6.golden b/pkg/test/testdata/no-to-ipv6.golden
index 38195c5..9cece1c 100644
--- a/pkg/test/testdata/no-to-ipv6.golden
+++ b/pkg/test/testdata/no-to-ipv6.golden
@@ -2,7 +2,7 @@ Mailbox: ip6recipient
 From: <fromuser@inbucket.org>
 To: [<ip6recipient@[IPv6:2001:0db8:85a3:0000:0000:8a2e:0370:7334]>]
 Subject: basic subject
-Size: 180
+Size: 218
 
 BODY TEXT:
 No-To message.