diff --git a/addons/mail/static/src/components/discuss/tests/discuss_tests.js b/addons/mail/static/src/components/discuss/tests/discuss_tests.js
index bc97a8c004b..5308ac818ea 100644
--- a/addons/mail/static/src/components/discuss/tests/discuss_tests.js
+++ b/addons/mail/static/src/components/discuss/tests/discuss_tests.js
@@ -1246,6 +1246,28 @@ QUnit.test('load single message from channel initially', async function (assert)
     );
 });
 
+QUnit.test('open channel from active_id as channel id', async function (assert) {
+    assert.expect(1);
+
+    this.data['mail.channel'].records.push({ id: 20 });
+    await this.start({
+        discuss: {
+            context: {
+                active_id: 20,
+            },
+        }
+    });
+    assert.containsOnce(
+        document.body,
+        `
+            .o_Discuss_thread[data-thread-local-id="${
+                this.env.models['mail.thread'].findFromIdentifyingData({ id: 20, model: 'mail.channel' }).localId
+            }"]
+        `,
+        "should have channel with ID 20 open in Discuss when providing active_id 20"
+    );
+});
+
 QUnit.test('basic rendering of message', async function (assert) {
     // AKU TODO: should be in message-only tests
     assert.expect(13);
diff --git a/addons/mail/static/src/components/discuss_mobile_mailbox_selection/discuss_mobile_mailbox_selection_tests.js b/addons/mail/static/src/components/discuss_mobile_mailbox_selection/discuss_mobile_mailbox_selection_tests.js
index 261d8c4bf54..0d145c13522 100644
--- a/addons/mail/static/src/components/discuss_mobile_mailbox_selection/discuss_mobile_mailbox_selection_tests.js
+++ b/addons/mail/static/src/components/discuss_mobile_mailbox_selection/discuss_mobile_mailbox_selection_tests.js
@@ -91,6 +91,38 @@ QUnit.test('select another mailbox', async function (assert) {
     );
 });
 
+QUnit.test('auto-select "Inbox" when discuss had channel as active thread', async function (assert) {
+    assert.expect(3);
+
+    this.data['mail.channel'].records.push({ id: 20 });
+    await this.start({
+        discuss: {
+            context: {
+                active_id: 20,
+            },
+        }
+    });
+    assert.hasClass(
+        document.querySelector('.o_MobileMessagingNavbar_tab[data-tab-id="channel"]'),
+        'o-active',
+        "'channel' tab should be active initially when loading discuss with channel id as active_id"
+    );
+
+    await afterNextRender(() => document.querySelector('.o_MobileMessagingNavbar_tab[data-tab-id="mailbox"]').click());
+    assert.hasClass(
+        document.querySelector('.o_MobileMessagingNavbar_tab[data-tab-id="mailbox"]'),
+        'o-active',
+        "'mailbox' tab should be selected after click on mailbox tab"
+    );
+    assert.hasClass(
+        document.querySelector(`.o_DiscussMobileMailboxSelection_button[data-mailbox-local-id="${
+            this.env.messaging.inbox.localId
+        }"]`),
+        'o-active',
+        "'Inbox' mailbox should be auto-selected after click on mailbox tab"
+    );
+});
+
 });
 });
 });
diff --git a/addons/mail/static/src/models/discuss/discuss.js b/addons/mail/static/src/models/discuss/discuss.js
index b05a08eea61..4bdc5e43549 100644
--- a/addons/mail/static/src/models/discuss/discuss.js
+++ b/addons/mail/static/src/models/discuss/discuss.js
@@ -151,7 +151,9 @@ function factory(dependencies) {
          * is not yet initialized.
          */
         openInitThread() {
-            const [model, id] = this.initActiveId.split('_');
+            const [model, id] = typeof this.initActiveId === 'number'
+                ? ['mail.channel', this.initActiveId]
+                : this.initActiveId.split('_');
             const thread = this.env.models['mail.thread'].findFromIdentifyingData({
                 id: model !== 'mail.box' ? Number(id) : id,
                 model,
@@ -160,6 +162,9 @@ function factory(dependencies) {
                 return;
             }
             thread.open();
+            if (this.env.messaging.device.isMobile && thread.channel_type) {
+                this.update({ activeMobileNavbarTabId: thread.channel_type });
+            }
         }
 
 
@@ -324,6 +329,18 @@ function factory(dependencies) {
          */
         _computeThread() {
             let thread = this.thread;
+            if (this.env.messaging &&
+                this.env.messaging.inbox &&
+                this.env.messaging.device.isMobile &&
+                this.activeMobileNavbarTabId === 'mailbox' &&
+                this.initActiveId !== 'mail.box_inbox' &&
+                !thread
+            ) {
+                // After loading Discuss from an arbitrary tab other then 'mailbox',
+                // switching to 'mailbox' requires to also set its inner-tab ;
+                // by default the 'inbox'.
+                return [['replace', this.env.messaging.inbox]];
+            }
             if (!thread || !thread.isPinned) {
                 return [['unlink']];
             }
@@ -396,7 +413,9 @@ function factory(dependencies) {
          * Formatted init thread on opening discuss for the first time,
          * when no active thread is defined. Useful to set a thread to
          * open without knowing its local id in advance.
-         * format: <threadModel>_<threadId>
+         * Support two formats:
+         *    {string} <threadModel>_<threadId>
+         *    {int} <channelId> with default model of 'mail.channel'
          */
         initActiveId: attr({
             default: 'mail.box_inbox',
@@ -450,6 +469,9 @@ function factory(dependencies) {
         messaging: one2one('mail.messaging', {
             inverse: 'discuss',
         }),
+        messagingInbox: many2one('mail.thread', {
+            related: 'messaging.inbox',
+        }),
         renamingThreads: one2many('mail.thread'),
         /**
          * The message that is currently selected as being replied to in Inbox.
@@ -497,8 +519,13 @@ function factory(dependencies) {
         thread: many2one('mail.thread', {
             compute: '_computeThread',
             dependencies: [
+                'activeMobileNavbarTabId',
+                'deviceIsMobile',
                 'isThreadPinned',
+                'messaging',
+                'messagingInbox',
                 'thread',
+                'threadModel',
             ],
         }),
         threadId: attr({