diff --git a/src/app/mailviewer/singlemailviewer.component.spec.ts b/src/app/mailviewer/singlemailviewer.component.spec.ts
index d4bc44f93..b2401c72c 100644
--- a/src/app/mailviewer/singlemailviewer.component.spec.ts
+++ b/src/app/mailviewer/singlemailviewer.component.spec.ts
@@ -18,6 +18,7 @@
 // ---------- END RUNBOX LICENSE ----------
 
 import { ComponentFixture, TestBed, tick, fakeAsync, waitForAsync, flush } from '@angular/core/testing';
+import { NgZone } from '@angular/core';
 
 import { SingleMailViewerComponent } from './singlemailviewer.component';
 import { ResizerModule } from '../directives/resizer.module';
@@ -231,6 +232,40 @@ describe('SingleMailViewerComponent', () => {
       expect(component.mailObj.attachments[1].downloadURL.indexOf('blob:')).toBe(0);
     }));
 
+  it('should not recalculate toolbar width during every change detection check', () => {
+    const calculateSpy = spyOn(component, 'calculateWidthDependentElements');
+
+    component.ngDoCheck();
+
+    expect(calculateSpy).not.toHaveBeenCalled();
+  });
+
+  it('should run toolbar resize recalculation inside Angular zone', () => {
+    const originalResizeObserver = window.ResizeObserver;
+    let resizeObserverCallback: ResizeObserverCallback;
+    (window as any).ResizeObserver = class {
+      constructor(callback: ResizeObserverCallback) {
+        resizeObserverCallback = callback;
+      }
+
+      observe() {}
+
+      disconnect() {}
+    };
+    const ngZone = TestBed.inject(NgZone);
+    const ngZoneRunSpy = spyOn(ngZone, 'run').and.callFake(<T>(callback: () => T) => callback());
+    const toolbarElement = document.createElement('div');
+
+    component.toolbarButtonContainer = {
+      nativeElement: toolbarElement
+    } as any;
+    resizeObserverCallback([], {} as ResizeObserver);
+
+    expect(ngZoneRunSpy).toHaveBeenCalled();
+
+    window.ResizeObserver = originalResizeObserver;
+  });
+
   describe('mailto: link interceptor', () => {
     let messageContentsElement: HTMLElement;
     let mailtoLink: HTMLAnchorElement;
diff --git a/src/app/mailviewer/singlemailviewer.component.ts b/src/app/mailviewer/singlemailviewer.component.ts
index 1bb81b032..53519f441 100644
--- a/src/app/mailviewer/singlemailviewer.component.ts
+++ b/src/app/mailviewer/singlemailviewer.component.ts
@@ -24,7 +24,9 @@ import {
   QueryList,
   ElementRef,
   AfterViewInit,
-  DoCheck
+  DoCheck,
+  OnDestroy,
+  NgZone
 } from '@angular/core';
 import { DomSanitizer } from '@angular/platform-browser';
 import DOMPurify from 'dompurify';
@@ -70,8 +72,10 @@ type Mail = any;
   templateUrl: 'singlemailviewer.component.html',
   styleUrls: ['singlemailviewer.component.scss']
 })
-export class SingleMailViewerComponent implements OnInit, DoCheck, AfterViewInit {
+export class SingleMailViewerComponent implements OnInit, DoCheck, AfterViewInit, OnDestroy {
   private lastMailtoInterceptorNode: HTMLElement | null = null;
+  private toolbarButtonContainerElement: ElementRef | null = null;
+  private toolbarResizeObserver: ResizeObserver | null = null;
 
 
   _messageId = null; // Message id or filename
@@ -96,7 +100,11 @@ export class SingleMailViewerComponent implements OnInit, DoCheck, AfterViewInit
   @ViewChildren('forwardMessageHeader', {read: ElementRef}) messageHeaderHTMLQuery: QueryList<ElementRef>;
   @ViewChild(HorizResizerDirective) resizer: HorizResizerDirective;
   @ViewChildren(HorizResizerDirective) resizerQuery: QueryList<HorizResizerDirective>;
-  @ViewChild('toolbarButtonContainer') toolbarButtonContainer: ElementRef;
+  @ViewChild('toolbarButtonContainer')
+  set toolbarButtonContainer(toolbarButtonContainer: ElementRef) {
+    this.toolbarButtonContainerElement = toolbarButtonContainer;
+    this.observeToolbarButtonContainer();
+  }
 
   public downloadProgress: number;
 
@@ -142,6 +150,7 @@ export class SingleMailViewerComponent implements OnInit, DoCheck, AfterViewInit
     private snackBar: MatSnackBar,
     private contactsservice: ContactsService,
     private preferenceService: PreferencesService,
+    private ngZone: NgZone,
   ) {
     DOMPurify.addHook('afterSanitizeAttributes', function (node) {
       // set all elements owning target to target=_blank
@@ -317,14 +326,34 @@ export class SingleMailViewerComponent implements OnInit, DoCheck, AfterViewInit
   }
 
   ngDoCheck() {
-    this.calculateWidthDependentElements();
     // Rebind mailto interceptor if the underlying message or HTML view changes
     this.initMailtoInterceptor();
   }
 
+  ngOnDestroy() {
+    this.toolbarResizeObserver?.disconnect();
+  }
+
+  private observeToolbarButtonContainer() {
+    this.toolbarResizeObserver?.disconnect();
+
+    if (!this.toolbarButtonContainerElement) return;
+
+    this.calculateWidthDependentElements();
+
+    if (typeof ResizeObserver === 'undefined') return;
+
+    this.toolbarResizeObserver = new ResizeObserver(() => {
+      this.ngZone.run(() => {
+        this.calculateWidthDependentElements();
+      });
+    });
+    this.toolbarResizeObserver.observe(this.toolbarButtonContainerElement.nativeElement as HTMLDivElement);
+  }
+
   calculateWidthDependentElements() {
-    if (this.toolbarButtonContainer) {
-      const toolbarwidth = (this.toolbarButtonContainer.nativeElement as HTMLDivElement).clientWidth;
+    if (this.toolbarButtonContainerElement) {
+      const toolbarwidth = (this.toolbarButtonContainerElement.nativeElement as HTMLDivElement).clientWidth;
       this.morebuttonindex = Math.floor(
         toolbarwidth / TOOLBAR_BUTTON_WIDTH
       ) - 1;