I have been asked to customize Outlook Web App page several time in past by some of my clients.
Customizing Outlook Web App (OWA) page in Exchange 2013 is easy as compare to other previous versions.
Default OWA login page is regular Blue and White theme.
You will have change few file to make Log In page the way you want it to look.
On Client Access Server you will have to browse the location where all the theme files are store.
C:Program FilesMicrosoftExchange ServerV15FrontEndHttpProxyowaauth15.0.995themes
Note: Before you make any changes to the existing files, make sure you take a backup of all the files by copying and pasting it some where on the server or on the network.
For this article I am making changes on 2 files which are highlighted olk_logo_white and owa_text_blue
Copy and paste the file and click on replace button once get the pop after pasting the file.
There’s one more location you can make the changes. In IIS you can do the same thing.
After making the changes you can login to the owa URL in my case its https://webmail.exchangeranger.net/owa and you should see the new owa login page.