File: //usr/share/webmin/virtual-server/help/template_webmaildom.html
<header>URL for webmail redirect</header>
By default, Virtualmin will redirect requests to <tt>http://webmail.thedomain.com</tt> to Usermin on the same system, like <tt>https://thedomain.com:20000/</tt>. However, this field can be used to change the redirect URL, perhaps to a single hostname for all your domains for which you have an SSL certificate, like
<tt>https://webmail.yourcompany.com:20000/</tt>. Or you can redirect to
another webmail application on the same domain, by entering a URL like
<tt>http://www.${DOM}/squirrelmail/</tt>. <p>
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