🔐 What Happens After OWA Login? Understanding Exchange OWA Customization Scope

In my previous blog, I explained how to customize the Exchange OWA login page — changing the favicon, title bar text, sidebar color, and default images like owa_text_blue.png and olk_logo_white.png.

But after logging in, I began to wonder:

“Will these customizations stay visible after login?”
“Can I customize the OWA mailbox interface too?”

Let’s explore what happens after users log in and what’s safe (and supported) to customize.

🎯 What We Customize in the Login Page

When customizing OWA, most of the work is done under this path:

C:\Program Files\Microsoft\Exchange Server\V15\FrontEnd\HttpProxy\owa\auth

From here, we can safely change:

The favicon.ico (browser tab icon)
The browser title (via logon.aspx)
Sidebar background colors
Login page images (e.g., owa_text_blue.png, olk_logo_white.png)
Custom text messages on the login screen

All these changes apply only to the pre-authentication experience — the login page users see before signing in.

🚪 What Happens After Login?

Once a user logs in, Exchange redirects them to the authenticated mailbox interface.

What I Customize after the Login Page?

C:\Program Files\Microsoft\Exchange Server\V15\ClientAccess\Owa

I replaced Favicon.ico file.

Restart with IISReset.

⚠️ Why You Should Avoid Customizing Post-Login OWA UI

Here’s what I discovered — and why I won’t touch this part:

🚫 Not Supported by Microsoft

Microsoft does not support customizing the post-login OWA experience.
Custom files may break after Cumulative Updates (CUs) or Security Patches.
If anything breaks, Microsoft support may decline to help you.

🧩 Complex and Minified Code

Post-login components are deeply embedded in minified JavaScript, bundled CSS, and complex layout engines.
Editing these files can easily cause OWA to crash or behave unexpectedly.

🔁 Updates Overwrite Everything

During CU updates, the ClientAccess\owa folder is often completely replaced.
Any changes here are lost, requiring tedious rework and re-testing.

🧠 Final Thoughts

Customizing the OWA login page is a great way to reinforce your organization’s branding — but it’s equally important to understand the boundary of what’s supported.

🎯 My approach: I focus on creating a clean, branded login page and leave the mailbox interface untouched for compatibility and support reasons.