diff --git a/addons/mail/static/src/components/composer/composer.xml b/addons/mail/static/src/components/composer/composer.xml
index ddd3368c21a..c85b5802863 100644
--- a/addons/mail/static/src/components/composer/composer.xml
+++ b/addons/mail/static/src/components/composer/composer.xml
@@ -83,6 +83,7 @@
                         t-on-o-composer-suggestion-clicked="_onComposerSuggestionClicked"
                         t-on-o-composer-text-input-send-shortcut="_onComposerTextInputSendShortcut"
                         t-on-paste="_onPasteTextInput"
+                        t-key="composer.localId"
                         t-ref="textInput"
                     />
                     <div class="o_Composer_buttons" t-att-class="{ 'o-composer-is-compact': props.isCompact, 'o-mobile': env.messaging.device.isMobile }">
diff --git a/addons/mail/static/src/components/composer_text_input/composer_text_input.js b/addons/mail/static/src/components/composer_text_input/composer_text_input.js
index 068bdd303d4..9921b2912ae 100644
--- a/addons/mail/static/src/components/composer_text_input/composer_text_input.js
+++ b/addons/mail/static/src/components/composer_text_input/composer_text_input.js
@@ -179,7 +179,7 @@ class ComposerTextInput extends Component {
      * @private
      */
     _onFocusinTextarea() {
-        this.composer.update({ hasFocus: true });
+        this.composer.focus();
     }
 
     /**
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 989bb75235e..77f7e875e42 100644
--- a/addons/mail/static/src/components/discuss/tests/discuss_tests.js
+++ b/addons/mail/static/src/components/discuss/tests/discuss_tests.js
@@ -4206,6 +4206,53 @@ QUnit.test('auto-focus composer on opening thread', async function (assert) {
     );
 });
 
+QUnit.test('mark channel as seen if last message is visible when switching channels when the previous channel had a more recent last message than the current channel', async function (assert) {
+    assert.expect(1);
+
+    this.data['mail.channel'].records.push(
+        { id: 10, message_unread_counter: 1, name: 'Bla' },
+        { id: 11, message_unread_counter: 1, name: 'Blu' },
+    );
+    this.data['mail.message'].records.push({
+        body: 'oldest message',
+        channel_ids: [10],
+        id: 10,
+    }, {
+        body: 'newest message',
+        channel_ids: [11],
+        id: 11,
+    });
+    await this.start({
+        discuss: {
+            context: {
+                active_id:  'mail.channel_11',
+            },
+        },
+    });
+    await afterNextRender(() => {
+        document.querySelector(`
+            .o_DiscussSidebar_item[data-thread-local-id="${
+                this.env.models['mail.thread'].findFromIdentifyingData({
+                    id: 10,
+                    model: 'mail.channel',
+                }).localId
+            }"]
+        `).click();
+    });
+    assert.doesNotHaveClass(
+        document.querySelector(`
+            .o_DiscussSidebar_item[data-thread-local-id="${
+                this.env.models['mail.thread'].findFromIdentifyingData({
+                    id: 10,
+                    model: 'mail.channel',
+                }).localId
+            }"]
+        `),
+        'o-unread',
+        "sidebar item of channel ID 10 should no longer be unread"
+    );
+});
+
 });
 });
 });
diff --git a/addons/mail/static/src/models/composer/composer.js b/addons/mail/static/src/models/composer/composer.js
index 25052fd1b38..0a1d817466e 100644
--- a/addons/mail/static/src/models/composer/composer.js
+++ b/addons/mail/static/src/models/composer/composer.js
@@ -102,6 +102,21 @@ function factory(dependencies) {
             }
         }
 
+        /**
+         * Focus this composer and remove focus from all others.
+         * Focus is a global concern, it makes no sense to have multiple composers focused at the
+         * same time.
+         */
+        focus() {
+            const allComposers = this.env.models['mail.composer'].all();
+            for (const otherComposer of allComposers) {
+                if (otherComposer !== this && otherComposer.hasFocus) {
+                    otherComposer.update({ hasFocus: false });
+                }
+            }
+            this.update({ hasFocus: true });
+        }
+
         /**
          * Inserts text content in text input based on selection.
          *
diff --git a/addons/mail/static/src/models/thread_view/thread_view.js b/addons/mail/static/src/models/thread_view/thread_view.js
index 6e875133a4b..895732f8872 100644
--- a/addons/mail/static/src/models/thread_view/thread_view.js
+++ b/addons/mail/static/src/models/thread_view/thread_view.js
@@ -136,6 +136,7 @@ function factory(dependencies) {
             if (this.threadCache) {
                 this.threadCache.update({ isCacheRefreshRequested: true });
             }
+            this.update({ lastVisibleMessage: [['unlink']] });
         }
 
         /**
@@ -225,12 +226,15 @@ function factory(dependencies) {
          * hint `message-received`.
          */
         hasAutoScrollOnMessageReceived: attr(),
+        /**
+         * Last message in the context of the currently displayed thread cache.
+         */
         lastMessage: many2one('mail.message', {
             related: 'thread.lastMessage',
         }),
         /**
          * Most recent message in this ThreadView that has been shown to the
-         * current partner.
+         * current partner in the currently displayed thread cache.
          */
         lastVisibleMessage: many2one('mail.message'),
         messages: many2many('mail.message', {