diff --git a/packages/transport/src/modules/messages/MessageController.ts b/packages/transport/src/modules/messages/MessageController.ts
index d5112cdc7..828abe5e1 100644
--- a/packages/transport/src/modules/messages/MessageController.ts
+++ b/packages/transport/src/modules/messages/MessageController.ts
@@ -387,14 +387,15 @@ export class MessageController extends TransportController {
     }
 
     public async validateMessageRecipients(recipients: CoreAddress[]): Promise<Result<void>> {
-        const peersWithNeitherActiveNorTerminatedRelationship: string[] = [];
+        const peersWithWrongRelationshipStatus: string[] = [];
         const deletedPeers: string[] = [];
 
         for (const recipient of recipients) {
             const relationship = await this.relationships.getRelationshipToIdentity(recipient);
 
-            if (!relationship || !(relationship.status === RelationshipStatus.Terminated || relationship.status === RelationshipStatus.Active)) {
-                peersWithNeitherActiveNorTerminatedRelationship.push(recipient.address);
+            const allowedRelationshipStatuses = [RelationshipStatus.Pending, RelationshipStatus.Active, RelationshipStatus.Terminated];
+            if (!relationship || !allowedRelationshipStatuses.includes(relationship.status)) {
+                peersWithWrongRelationshipStatus.push(recipient.address);
                 continue;
             }
 
@@ -403,8 +404,9 @@ export class MessageController extends TransportController {
             }
         }
 
-        if (peersWithNeitherActiveNorTerminatedRelationship.length > 0) {
-            return Result.fail(TransportCoreErrors.messages.hasNeitherActiveNorTerminatedRelationship(peersWithNeitherActiveNorTerminatedRelationship));
+        if (peersWithWrongRelationshipStatus.length > 0) {
+            // TODO: rename error
+            return Result.fail(TransportCoreErrors.messages.hasNeitherActiveNorTerminatedRelationship(peersWithWrongRelationshipStatus));
         }
 
         if (deletedPeers.length > 0) return Result.fail(TransportCoreErrors.messages.peerIsDeleted(deletedPeers));
diff --git a/packages/transport/test/modules/messages/MessageController.test.ts b/packages/transport/test/modules/messages/MessageController.test.ts
index 3889da708..ee5b5eb13 100644
--- a/packages/transport/test/modules/messages/MessageController.test.ts
+++ b/packages/transport/test/modules/messages/MessageController.test.ts
@@ -1,4 +1,5 @@
 import { IDatabaseConnection } from "@js-soft/docdb-access-abstractions";
+import { Serializable } from "@js-soft/ts-serval";
 import { CoreDate, CoreId } from "@nmshd/core-types";
 import { AccountController, IdentityDeletionProcess, IdentityDeletionProcessStatus, Message, Relationship, RelationshipStatus, Transport } from "../../../src";
 import { TestUtil } from "../../testHelpers/TestUtil";
@@ -57,7 +58,7 @@ describe("MessageController", function () {
         await connection.close();
     });
 
-    describe("Sending Messages requires existence of active or terminated Relationship", function () {
+    describe("Sending Messages requires existence of pending, active or terminated Relationship", function () {
         beforeEach(async () => {
             const relationshipBetweenSenderAndRecipient3 = await sender.relationships.getRelationshipToIdentity(recipient3.identity.address);
 
@@ -85,13 +86,6 @@ describe("MessageController", function () {
             await expect(TestUtil.sendMessage(sender, recipient3)).rejects.toThrow("error.transport.messages.hasNeitherActiveNorTerminatedRelationship");
         });
 
-        test("cannot send Message for pending Relationship", async function () {
-            const pendingRelationship = await TestUtil.addPendingRelationship(sender, recipient3);
-            expect(pendingRelationship.status).toBe("Pending");
-
-            await expect(TestUtil.sendMessage(sender, recipient3)).rejects.toThrow("error.transport.messages.hasNeitherActiveNorTerminatedRelationship");
-        });
-
         test("cannot send Message for Relationship whose deletion is proposed", async function () {
             await TestUtil.addRelationship(sender, recipient3);
             await TestUtil.terminateRelationship(recipient3, sender);
@@ -267,6 +261,50 @@ describe("MessageController", function () {
         });
     });
 
+    describe("Sending and decrypting Messages for pending Relationships", function () {
+        let recipientWithPendingRelationship: AccountController;
+        let pendingRelationship: Relationship;
+
+        beforeEach(async function () {
+            recipientWithPendingRelationship = (await TestUtil.provideAccounts(transport, connection, 1))[0];
+            pendingRelationship = await TestUtil.addPendingRelationship(sender, recipientWithPendingRelationship);
+        });
+
+        afterEach(async () => await recipientWithPendingRelationship.close());
+
+        test("should be able to send a Message on a pending Relationship as the templator", async function () {
+            await expect(
+                sender.messages.sendMessage({ recipients: [recipientWithPendingRelationship.identity.address], content: Serializable.fromAny({ content: "TestContent" }) })
+            ).resolves.not.toThrow();
+        });
+
+        test("should be able to send a Message on a pending Relationship as the requestor", async function () {
+            await expect(
+                recipientWithPendingRelationship.messages.sendMessage({ recipients: [sender.identity.address], content: Serializable.fromAny({ content: "TestContent" }) })
+            ).resolves.not.toThrow();
+        });
+
+        test("should be able to receive a Message sent on a pending Relationship as a tempator after the Relationship was activated", async function () {
+            const idOfSentMessageDuringPendingRelationship = (await TestUtil.sendMessage(sender, recipientWithPendingRelationship)).id;
+
+            await TestUtil.acceptPendingRelationship(sender, recipientWithPendingRelationship, pendingRelationship);
+
+            const receivedMessages = await TestUtil.syncUntilHasMessages(recipientWithPendingRelationship);
+            const idOfReceivedMessageAfterActivation = receivedMessages[receivedMessages.length - 1].id;
+            expect(idOfReceivedMessageAfterActivation).toStrictEqual(idOfSentMessageDuringPendingRelationship);
+        });
+
+        test("should be able to receive a Message sent on a pending Relationship as a requestor after the Relationship was activated", async function () {
+            const idOfSentMessageDuringPendingRelationship2 = (await TestUtil.sendMessage(recipientWithPendingRelationship, sender)).id;
+
+            await TestUtil.acceptPendingRelationship(sender, recipientWithPendingRelationship, pendingRelationship);
+
+            const receivedMessages2 = await TestUtil.syncUntilHasMessages(sender);
+            const idOfReceivedMessageAfterActivation2 = receivedMessages2[receivedMessages2.length - 1].id;
+            expect(idOfReceivedMessageAfterActivation2).toStrictEqual(idOfSentMessageDuringPendingRelationship2);
+        });
+    });
+
     describe("Sending and decrypting Messages for terminated Relationships", function () {
         let messageExchangedBeforeTermination: Message;
 
diff --git a/packages/transport/test/testHelpers/TestUtil.ts b/packages/transport/test/testHelpers/TestUtil.ts
index 6d9e02793..274ea2bb8 100644
--- a/packages/transport/test/testHelpers/TestUtil.ts
+++ b/packages/transport/test/testHelpers/TestUtil.ts
@@ -9,6 +9,7 @@ import { ISerializable, Serializable } from "@js-soft/ts-serval";
 import { EventEmitter2EventBus, sleep } from "@js-soft/ts-utils";
 import { CoreAddress, CoreDate, CoreId } from "@nmshd/core-types";
 import { CoreBuffer } from "@nmshd/crypto";
+import { assert } from "console";
 import fs from "fs";
 import { DurationLike } from "luxon";
 import path from "path";
@@ -394,7 +395,17 @@ export class TestUtil {
     ): Promise<{ acceptedRelationshipFromSelf: Relationship; acceptedRelationshipPeer: Relationship }> {
         const pendingRelationshipFromSelf = await TestUtil.addPendingRelationship(from, to, template);
 
-        const acceptedRelationshipFromSelf = await from.relationships.accept(pendingRelationshipFromSelf.id);
+        return await this.acceptPendingRelationship(from, to, pendingRelationshipFromSelf);
+    }
+
+    public static async acceptPendingRelationship(
+        from: AccountController,
+        to: AccountController,
+        pendingRelationship: Relationship
+    ): Promise<{ acceptedRelationshipFromSelf: Relationship; acceptedRelationshipPeer: Relationship }> {
+        assert(pendingRelationship.status === RelationshipStatus.Pending);
+
+        const acceptedRelationshipFromSelf = await from.relationships.accept(pendingRelationship.id);
         expect(acceptedRelationshipFromSelf.status).toStrictEqual(RelationshipStatus.Active);
 
         // Get accepted relationship