when a customer types in www.theirdomain.com/webmail and logs in they get a multi-client selector page for neomail, horde and squirrelmail.

I want to slowly phase out neomail so I would like to edit that page that comes up to warn people that neomail is being removed.

What html or cgi program/page or file is that. Can it be manually edited to add a bit of text below the selection so I can warn them?.