diff --git a/addons/mail/static/src/core/common/suggestion_service.js b/addons/mail/static/src/core/common/suggestion_service.js
index 2a4a8a3e5db..32d2dc2ff3c 100644
--- a/addons/mail/static/src/core/common/suggestion_service.js
+++ b/addons/mail/static/src/core/common/suggestion_service.js
@@ -208,8 +208,9 @@ export class SuggestionService {
                 }
             }
             if (thread) {
-                const isFollower1 = thread.followers.some((follower) => follower.partner === p1);
-                const isFollower2 = thread.followers.some((follower) => follower.partner === p2);
+                const followerList = [...thread.followers];
+                const isFollower1 = followerList.some((follower) => follower.partner === p1);
+                const isFollower2 = followerList.some((follower) => follower.partner === p2);
                 if (isFollower1 && !isFollower2) {
                     return -1;
                 }
diff --git a/addons/mail/static/src/core/common/thread_model.js b/addons/mail/static/src/core/common/thread_model.js
index b7e2732204a..a4697fcf301 100644
--- a/addons/mail/static/src/core/common/thread_model.js
+++ b/addons/mail/static/src/core/common/thread_model.js
@@ -51,8 +51,8 @@ export class Thread {
     customName;
     /** @type {string} */
     description;
-    /** @type {import("@mail/core/common/follower_model").Follower[]} */
-    followers = [];
+    /** @type {Set<import("@mail/core/common/follower_model").Follower>} */
+    followers = new Set();
     isAdmin = false;
     loadOlder = false;
     loadNewer = false;
@@ -256,7 +256,12 @@ export class Thread {
      * @returns {import("@mail/core/common/follower_model").Follower}
      */
     get followerOfSelf() {
-        return this.followers.find((f) => f.partner === this._store.self);
+        for (const follower of this.followers) {
+            if (follower.partner === this._store.self) {
+                return follower;
+            }
+        }
+        return undefined;
     }
 
     get imgUrl() {
diff --git a/addons/mail/static/src/core/web/chatter.js b/addons/mail/static/src/core/web/chatter.js
index 3b3427f4a2c..7418feddb4b 100644
--- a/addons/mail/static/src/core/web/chatter.js
+++ b/addons/mail/static/src/core/web/chatter.js
@@ -201,7 +201,7 @@ export class Chatter extends Component {
      * @returns {string}
      */
     get toRecipientsText() {
-        const followers = this.state.thread.followers.slice(0, 5).map(({ partner }) => {
+        const followers = [...this.state.thread.followers].slice(0, 5).map(({ partner }) => {
             if (partner === this.store.self) {
                 return `<span class="text-muted" title="${escape(partner.email)}">me</span>`;
             }
@@ -213,7 +213,7 @@ export class Chatter extends Component {
             this.store.env.services["user"].lang?.replace("_", "-"),
             { type: "unit" }
         );
-        if (this.state.thread.followers.length > 5) {
+        if (this.state.thread.followers.size > 5) {
             followers.push("…");
         }
         return markup(formatter.format(followers));
diff --git a/addons/mail/static/src/core/web/chatter.xml b/addons/mail/static/src/core/web/chatter.xml
index c9403fec8d4..34e2a9ebe30 100644
--- a/addons/mail/static/src/core/web/chatter.xml
+++ b/addons/mail/static/src/core/web/chatter.xml
@@ -35,17 +35,17 @@
                     <Dropdown t-if="props.hasFollowers" position="'bottom-end'" disabled="isDisabled" class="'o-mail-Followers d-flex me-1'" menuClass="'o-mail-Followers-dropdown flex-column p-0'" menuDisplay="'d-flex'" title="followerButtonLabel" togglerClass="'o-mail-Followers-button btn btn-link text-action px-1 ' + (props.compactHeight ? '' : 'my-2')">
                         <t t-set-slot="toggler">
                             <i class="fa fa-user-o" role="img"/>
-                            <span class="o-mail-Followers-counter ps-1" t-esc="state.thread.followers.length"/>
+                            <span class="o-mail-Followers-counter ps-1" t-esc="state.thread.followers.size"/>
                         </t>
                         <t t-set-slot="default">
                             <t t-if="state.thread.hasWriteAccess">
                                 <a class="dropdown-item" href="#" role="menuitem" t-on-click.prevent="onClickAddFollowers">
                                     Add Followers
                                 </a>
-                                <div t-if="state.thread.followers.length > 0" role="separator" class="dropdown-divider"/>
+                                <div t-if="state.thread.followers.size > 0" role="separator" class="dropdown-divider"/>
                             </t>
-                            <t t-if="state.thread.followers.length > 0">
-                                <div t-foreach="state.thread.followers" t-as="follower" t-key="follower.id" class="dropdown-item o-mail-Follower d-flex justify-content-between p-0">
+                            <t t-if="state.thread.followers.size > 0">
+                                <div t-foreach="[...state.thread.followers]" t-as="follower" t-key="follower.id" class="dropdown-item o-mail-Follower d-flex justify-content-between p-0">
                                     <a class="o-mail-Follower-details d-flex align-items-center flex-grow-1 px-3 text-700 o-min-width-0" t-att-class="{ 'o-inactive fst-italic opacity-25': !follower.isActive }" href="#" role="menuitem" t-on-click.prevent="(ev) => this.onClickDetails(ev, follower)">
                                         <img class="o-mail-Follower-avatar me-2 rounded" t-att-src="threadService.avatarUrl(follower.partner, state.thread)" alt=""/>
                                         <span class="flex-shrink text-truncate" t-esc="follower.partner.name"/>
@@ -92,7 +92,7 @@
                 </button>
             </div>
             <t t-if="state.thread.composer.type">
-                <t t-if="state.thread.composer.type === 'message' and state.thread.followers.length > 0">
+                <t t-if="state.thread.composer.type === 'message' and state.thread.followers.size > 0">
                     <div class="flex-shrink-0 px-3 pt-3 text-truncate small mb-2" style="margin-left:48px">
                         <span class="fw-bold">To:</span> <t t-out="toRecipientsText"/>
                         <button class="o-mail-Chatter-recipientListButton btn btn-link badge rounded-pill border-0 p-1 ms-1" title="Show all recipients" t-on-click="onClickRecipientList">
diff --git a/addons/mail/static/src/core/web/recipient_list.xml b/addons/mail/static/src/core/web/recipient_list.xml
index 6a5397e59e7..c9a6062096b 100644
--- a/addons/mail/static/src/core/web/recipient_list.xml
+++ b/addons/mail/static/src/core/web/recipient_list.xml
@@ -4,7 +4,7 @@
     <t t-name="mail.RecipientList" owl="1">
         <div class="o-mail-RecipientList p-2 overflow-auto">
             <ul class="list-unstyled mb-0">
-                <li t-foreach="props.thread.followers" t-as="follower" t-key="follower.id">
+                <li t-foreach="[...props.thread.followers]" t-as="follower" t-key="follower.id">
                     <t t-out="follower.partner.email"/>
                 </li>
             </ul>
diff --git a/addons/mail/static/src/core/web/thread_service_patch.js b/addons/mail/static/src/core/web/thread_service_patch.js
index 869c6ef5162..c9fcc9d6727 100644
--- a/addons/mail/static/src/core/web/thread_service_patch.js
+++ b/addons/mail/static/src/core/web/thread_service_patch.js
@@ -138,9 +138,7 @@ patch(ThreadService.prototype, "mail/core/web", {
             partner: this.personaService.insert({ ...data.partner, type: "partner" }),
             _store: this.store,
         });
-        if (!follower.followedThread.followers.includes(follower)) {
-            follower.followedThread.followers.push(follower);
-        }
+        follower.followedThread.followers.add(follower);
         return follower;
     },
     /**
@@ -190,10 +188,7 @@ patch(ThreadService.prototype, "mail/core/web", {
             [follower.followedThread.id],
             [follower.partner.id],
         ]);
-        const index = follower.followedThread.followers.indexOf(follower);
-        if (index !== -1) {
-            follower.followedThread.followers.splice(index, 1);
-        }
+        follower.followedThread.followers.delete(follower);
         delete this.store.followers[follower.id];
     },
     unpin(thread) {