Per the support KB, Microsoft PSS has the support policy for customization of Outlook Web Access for Exchange that cover its versions like 5.5, 2000 & 2003.
Per the article, we can get more information regarding the support policy for OWA customization for its various versions like,
“…The Exchange 5.5 version of OWA is made up of Active Server Pages (ASPs).
The Exchange 2000 and Exchange 2003 versions of OWA are composed of two main components: templates and controls. Templates are served from a binary Internet Server Application Programming Interface (ISAPI) extension that communicates with the Exchange store. Controls are referenced by the templates and are located in the Program Files\Exchsrvr\Exchweb folder. Controls are made up of script or HTML files, such as JScript files (.js), HTML Component files (.htc), cascading style sheet files (.css), Extensible Stylesheet Language (XSL) transform files (.xsl), and graphics files.
You may want to customize OWA by changing features or by modifying the user interface or by using the article. Although you can customize OWA objects by modifying either the script code or the HTML, Microsoft does not recommend that you do so. Microsoft Product Support Services (PSS) also cannot help you with the customization. However, if you want to customize OWA, the following limitations and considerations apply:
- PSS does not provide assistance to customize OWA objects.
- If you contact PSS about an OWA issue for a server that OWA is customized on, you must replace the customized files with the original versions of the files and verify that you can reproduce the issue by using the original versions of the files. If the issue occurs only with the customized versions of the files, and you cannot reproduce the issue with the original versions of the files, PSS cannot help you troubleshoot the issue.
- If you install a service pack or hotfix that updates the files in the Program Files\Exchsrvr\Exchweb folder, any customized files that exist in that folder are overwritten. If you do not want to lose the customizations that you created, create a backup of the customized files, and then restore the files after you install the service pack or hotfix.
Although PSS cannot help you customize OWA, the following resources are available:
- Microsoft hosts public newsgroups where you can post questions and discuss topics that are related to Exchange Server or Exchange 2000. One of the newsgroups where you can ask questions that are related to Exchange 2000 development is “microsoft.public.exchange2000.development”. To access this newsgroup and other Exchange Server newsgroups, visit the following Microsoft Web site:
- To locate other Exchange Server communities, visit the following Microsoft Web site:
But still lot of guys around the world customize the OWA though.
You can find the following article,
Customizing the Outlook Web Access Logon Page
Still want to customize the CSS and Dynamic styles, you can refer these articles,
W3C: Cascading Style Sheets Home Page
W3C: Adding a Touch of Style
W3C: Cascading Style Sheets, level 2: CSS2 Specification
MSDN: Introduction to Dynamic Styles
Hope this helps!!