diff --git a/addons/mail/static/src/js/thread_field.js b/addons/mail/static/src/js/thread_field.js
index ab8023b06ad..ea64d1fc9e3 100644
--- a/addons/mail/static/src/js/thread_field.js
+++ b/addons/mail/static/src/js/thread_field.js
@@ -43,6 +43,7 @@ var ThreadField = AbstractField.extend({
             displayOrder: ThreadWidget.ORDER.DESC,
             displayDocumentLinks: false,
             displayMarkAsRead: false,
+            hasMessageAttachmentDeletable: true,
             squashCloseMessages: false,
         });
 
diff --git a/addons/mail/static/src/js/thread_widget.js b/addons/mail/static/src/js/thread_widget.js
index e5902602a77..9550931ad95 100644
--- a/addons/mail/static/src/js/thread_widget.js
+++ b/addons/mail/static/src/js/thread_widget.js
@@ -68,6 +68,7 @@ var ThreadWidget = Widget.extend({
             displayEmailIcons: true,
             displayReplyIcons: false,
             loadMoreOnScroll: false,
+            hasMessageAttachmentDeletable: false,
         });
         // options when the thread is disabled
         this._disabledOptions = {
@@ -81,6 +82,7 @@ var ThreadWidget = Widget.extend({
             displayEmailIcons: false,
             displayReplyIcons: false,
             loadMoreOnScroll: this._enabledOptions.loadMoreOnScroll,
+            hasMessageAttachmentDeletable: false,
         };
         this._selectedMessageID = null;
         this._currentThreadID = null;
diff --git a/addons/mail/static/src/xml/thread.xml b/addons/mail/static/src/xml/thread.xml
index ef21b2c5ede..12d41ebd431 100644
--- a/addons/mail/static/src/xml/thread.xml
+++ b/addons/mail/static/src/xml/thread.xml
@@ -254,6 +254,7 @@
         @param {boolean} [options.displayReplyIcons]
         @param {boolean} [options.displayStars]
         @param {boolean} [options.displaySubjectsOnMessages]
+        @param {boolean} options.hasMessageAttachmentDeletable
         @param {string|integer} [options.messagesSeparatorPosition] 'top' or
             message ID, the separator is placed just after this message.
         @param {integer} [options.selectedMessageID]
@@ -354,12 +355,16 @@
                     <t t-if="message.hasAttachments()">
                         <div t-if="message.hasImageAttachments()" class="o_attachments_previews">
                             <t t-foreach="message.getImageAttachments()" t-as="attachment">
-                                <t t-call="mail.AttachmentPreview"/>
+                                <t t-call="mail.AttachmentPreview">
+                                    <t t-set="isDeletable" t-value="options.hasMessageAttachmentDeletable"/>
+                                </t>
                             </t>
                         </div>
                         <div t-if="message.hasNonImageAttachments()" class="o_attachments_list">
                             <t t-foreach="message.getNonImageAttachments()" t-as="attachment">
-                                <t t-call="mail.Attachment"/>
+                                <t t-call="mail.Attachment">
+                                    <t t-set="isDeletable" t-value="options.hasMessageAttachmentDeletable"/>
+                                </t>
                             </t>
                         </div>
                     </t>
@@ -526,6 +531,7 @@
         @param {integer} attachment.id
         @param {string} attachment.name
         @param {string} attachment.url
+        @param {boolean} [isDeletable=false]
     -->
     <t t-name="mail.AttachmentPreview">
         <div class="o_attachment" t-att-title="attachment.name">
@@ -533,7 +539,7 @@
                 <div class="o_image_box">
                     <div class="o_attachment_image" t-attf-style="background-image:url('/web/image/#{attachment.id}/160x160/?crop=true')"/>
                     <div t-attf-class="o_image_overlay o_attachment_view"  t-att-data-id="attachment.id">
-                        <span class="fa fa-times o_attachment_delete_cross" t-att-title="'Delete ' + attachment.name" t-att-data-id="attachment.id" t-att-data-name="attachment.name"/>
+                        <span t-if="isDeletable" class="fa fa-times o_attachment_delete_cross" t-att-title="'Delete ' + attachment.name" t-att-data-id="attachment.id" t-att-data-name="attachment.name"/>
                         <span class="o_attachment_title text-white"><t t-esc="attachment.name"/></span>
                         <a class="o_attachment_download" t-att-href='attachment.url'>
                             <i t-attf-class="fa fa-download text-white" t-att-title="'Download ' + attachment.name" role="img" aria-label="Download"></i>
@@ -552,12 +558,15 @@
         @param {string} attachment.name
         @param {boolean} attachment.upload
         @param {string} attachment.url
+        @param {boolean} [editable=false] if set, it means the attachment is rendered in the composer.
+          Some changes are required in that case, such as "delete" button is not visible (pretty unlink is used instead).
+        @param {boolean} [isDeletable=false]
     -->
     <t t-name="mail.Attachment">
         <t t-set="type" t-value="attachment.mimetype and attachment.mimetype.split('/').shift()"/>
         <div t-attf-class="o_attachment #{ editable ? 'o_attachment_editable' : '' } #{attachment.upload ? 'o_attachment_uploading' : ''}" t-att-title="attachment.name">
             <div class="o_attachment_wrap">
-                <span t-if="!editable" class="fa fa-times o_attachment_delete_cross" t-att-title="'Delete ' + attachment.name" t-att-data-id="attachment.id" t-att-data-name="attachment.name"/>
+                <span t-if="!editable and isDeletable" class="fa fa-times o_attachment_delete_cross" t-att-title="'Delete ' + attachment.name" t-att-data-id="attachment.id" t-att-data-name="attachment.name"/>
                 <t t-set="has_preview" t-value="type == 'image' or type == 'video' or attachment.mimetype == 'application/pdf'"/>
                 <t t-set="ext" t-value="attachment.filename.split('.').pop()"/>
 
diff --git a/addons/mail/static/tests/discuss_tests.js b/addons/mail/static/tests/discuss_tests.js
index 9949af7c28c..990f321a39d 100644
--- a/addons/mail/static/tests/discuss_tests.js
+++ b/addons/mail/static/tests/discuss_tests.js
@@ -1119,6 +1119,53 @@ QUnit.test('drag and drop file in composer [REQUIRE NON-INCOGNITO WINDOW]', asyn
     discuss.destroy();
 });
 
+QUnit.test('non-deletable message attachments', async function (assert) {
+    assert.expect(2);
+
+    this.data['mail.message'].records = [{
+        attachment_ids: [{
+            filename: "text.txt",
+            id: 250,
+            mimetype: 'text/plain',
+            name: "text.txt",
+        }, {
+            filename: "image.png",
+            id: 251,
+            mimetype: 'image/png',
+            name: "image.png",
+        }],
+        author_id: [5, "Demo User"],
+        body: "<p>test</p>",
+        id: 1,
+        needaction: true,
+        needaction_partner_ids: [3],
+        model: 'some.document',
+        record_name: "SomeDocument",
+        res_id: 100,
+    }];
+
+    const discuss = await createDiscuss({
+        context: {},
+        data: this.data,
+        params: {},
+        services: this.services,
+        session: {
+            partner_id: 3,
+        },
+    });
+    assert.containsN(
+        discuss,
+        '.o_attachment',
+        2,
+        "should display 2 attachments");
+    assert.containsNone(
+        discuss.$('.o_attachment'),
+        'o_attachment_delete_cross',
+        "attachments should not be deletable");
+
+    discuss.destroy();
+});
+
 QUnit.test('reply to message from inbox', async function (assert) {
     assert.expect(11);
 
diff --git a/addons/mail/static/tests/thread_window/basic_thread_window_tests.js b/addons/mail/static/tests/thread_window/basic_thread_window_tests.js
index 3200ae38d85..3dc8ac0336d 100644
--- a/addons/mail/static/tests/thread_window/basic_thread_window_tests.js
+++ b/addons/mail/static/tests/thread_window/basic_thread_window_tests.js
@@ -850,6 +850,59 @@ QUnit.test('receive 2 new DM messages in quick succession (no chat window initia
     parent.destroy();
 });
 
+QUnit.test('non-deletable message attachments', async function (assert) {
+    assert.expect(3);
+
+    this.data['mail.channel'].records = [{
+        id: 1,
+        name: "General",
+        channel_type: 'channel',
+    }];
+    this.data['mail.message'].records = [{
+        attachment_ids: [{
+            filename: "text.txt",
+            id: 250,
+            mimetype: 'text/plain',
+            name: "text.txt",
+        }, {
+            filename: "image.png",
+            id: 251,
+            mimetype: 'image/png',
+            name: "image.png",
+        }],
+        author_id: [5, "Demo User"],
+        body: "<p>test</p>",
+        channel_ids: [1],
+        id: 100,
+        model: 'mail.channel',
+        record_name: "general",
+        res_id: 1,
+    }];
+    const parent = this.createParent({
+        data: this.data,
+        services: this.services,
+    });
+    await testUtils.nextTick();
+    const channel = parent.call('mail_service', 'getChannel', 1);
+    channel.detach();
+    await testUtils.nextTick();
+    assert.containsOnce(
+        $,
+        '.o_thread_window',
+        "a thread window should be open");
+    assert.containsN(
+        $('.o_thread_window'),
+        '.o_attachment',
+        2,
+        "thread window should have 2 attachments");
+    assert.containsNone(
+        $('.o_thread_window .o_attachment'),
+        'o_attachment_delete_cross',
+        "attachments should not be deletable");
+
+    parent.destroy();
+});
+
 });
 });
 });