diff --git a/src/js/channels/MessageFlow.js b/src/js/channels/MessageFlow.js
index bf2f9eb..8cf0e20 100644
--- a/src/js/channels/MessageFlow.js
+++ b/src/js/channels/MessageFlow.js
@@ -16,6 +16,7 @@ import { mediaController } from '../media.js';
 import { adminStatePoller } from '../adminStatePoller.js';
 import { messageTime } from '../utils/messageTime.js';
 import { storageFetch } from '../storageFetch.js';
+import { NO_NETWORK, isOffline } from '../utils/network.js';
 
 export class MessageFlow {
     /**
@@ -653,6 +654,7 @@ export class MessageFlow {
         delete message.undelivered;
         let published;
         try {
+            if (isOffline()) throw new Error(NO_NETWORK);
             await this.manager.rotationRetry?.settle(messageStreamId);
             published = await this.manager.publishWithRetry(messageStreamId, message, channel.password);
         } catch (error) {
@@ -695,6 +697,7 @@ export class MessageFlow {
         if (!currentAddress) {
             throw new Error('Not authenticated');
         }
+        if (isOffline()) return;
 
         let canPublish = false;
         const cacheValid = channel._publishPermCache?.address?.toLowerCase() === currentAddress.toLowerCase() &&
diff --git a/src/js/dm.js b/src/js/dm.js
index b46fdd6..08e31a6 100644
--- a/src/js/dm.js
+++ b/src/js/dm.js
@@ -18,6 +18,7 @@ import { Logger } from './logger.js';
 import { applyAccount, stripLocalFields, dropLocalState } from './publisherProof.js';
 import { CONFIG } from './config.js';
 import { CryptoError } from './utils/errors.js';
+import { NO_NETWORK, isOffline } from './utils/network.js';
 import { streamrController, STREAM_CONFIG } from './streamr.js';
 import { channelManager } from './channels.js';
 import { secureStorage } from './secureStorage.js';
@@ -1347,6 +1348,7 @@ class DMManager {
     async _publishDm(channel, message) {
         const peerInboxStreamId = channel.messageStreamId;
         try {
+            if (isOffline()) throw new Error(NO_NETWORK);
             // E2E encrypt before publishing — NEVER send plaintext DMs
             const privateKey = authManager.wallet?.privateKey;
             const peerAddress = channel.peerAddress;
diff --git a/src/js/utils/network.js b/src/js/utils/network.js
new file mode 100644
index 0000000..7bb4e79
--- /dev/null
+++ b/src/js/utils/network.js
@@ -0,0 +1,6 @@
+export const NO_NETWORK = 'No network connection';
+
+/** True only when the browser reports no network at all; `onLine === true` proves nothing. */
+export function isOffline() {
+    return typeof navigator !== 'undefined' && navigator.onLine === false;
+}
diff --git a/tests/unit/channels.extended.test.js b/tests/unit/channels.extended.test.js
index 6675000..f91d992 100644
--- a/tests/unit/channels.extended.test.js
+++ b/tests/unit/channels.extended.test.js
@@ -611,6 +611,50 @@ describe('ChannelManager Extended', () => {
     });
 
     // ==================== updateMemberPermissions ====================
+    describe('sending with no network', () => {
+        const streamId = 'stream-offline-send';
+        let channel;
+        let offline;
+
+        beforeEach(() => {
+            channel = {
+                messageStreamId: streamId,
+                streamId,
+                type: 'public',
+                members: ['0xmyaddress'],
+                messages: [],
+                reactions: {},
+                password: null,
+                ephemeralStreamId: `${streamId}-ephemeral`,
+                createdBy: '0xmyaddress'
+            };
+            channelManager.channels.set(streamId, channel);
+            identityManager.resolveENS = vi.fn().mockResolvedValue(null);
+            offline = vi.spyOn(navigator, 'onLine', 'get').mockReturnValue(false);
+        });
+
+        afterEach(() => {
+            offline.mockRestore();
+            delete identityManager.resolveENS;
+        });
+
+        it('fails at once, keeps the message for Retry, and publishes it once the network is back', async () => {
+            const { NO_NETWORK } = await import('../../src/js/utils/network.js');
+            const publish = vi.spyOn(channelManager, 'publishWithRetry').mockResolvedValue(undefined);
+
+            await expect(channelManager.sendMessage(streamId, 'hello')).rejects.toThrow(NO_NETWORK);
+            expect(channel.messages[0]).toMatchObject({ text: 'hello', pending: false, failed: true, failError: NO_NETWORK });
+
+            await expect(channelManager.resendMessage(streamId, channel.messages[0].id)).rejects.toThrow(NO_NETWORK);
+            expect(publish).not.toHaveBeenCalled();
+
+            offline.mockReturnValue(true);
+            await channelManager.resendMessage(streamId, channel.messages[0].id);
+            expect(publish).toHaveBeenCalledTimes(1);
+            expect(channel.messages[0]).toMatchObject({ failed: false });
+        });
+    });
+
     describe('updateMemberPermissions', () => {
         const streamId = 'stream-gated-3';
 
diff --git a/tests/unit/dm.test.js b/tests/unit/dm.test.js
index 7bad2c4..6be9b42 100644
--- a/tests/unit/dm.test.js
+++ b/tests/unit/dm.test.js
@@ -1278,6 +1278,24 @@ describe('DMManager', () => {
             );
         });
 
+        it('fails at once with no network, without sealing or publishing', async () => {
+            const { NO_NETWORK } = await import('../../src/js/utils/network.js');
+            const peerAddress = '0xpeercccccccccccccccccccccccccccccccccccc';
+            const streamId = `${peerAddress}/Pombo-DM-1`;
+            const channel = { messageStreamId: streamId, type: 'dm', peerAddress, messages: [] };
+            channelManager.channels.set(streamId, channel);
+            const offline = vi.spyOn(navigator, 'onLine', 'get').mockReturnValue(false);
+            try {
+                await expect(dmManager.sendMessage(streamId, 'Hello')).rejects.toThrow(NO_NETWORK);
+            } finally {
+                offline.mockRestore();
+            }
+
+            expect(channel.messages[0]).toMatchObject({ pending: false, failed: true, failError: NO_NETWORK });
+            expect(dmCrypto.seal).not.toHaveBeenCalled();
+            expect(streamrController.publishAs).not.toHaveBeenCalled();
+        });
+
         it('marks a failed DM and resends it under the same id', async () => {
             const peerAddress = '0xpeeraaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa';
             const streamId = `${peerAddress}/Pombo-DM-1`;