By default, Virtualmin will redirect requests to `http://webmail.thedomain.com` to Usermin on the same system, like `https://thedomain.com:20000/`. 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 `https://webmail.yourcompany.com:20000/`. Or you can redirect to another webmail application on the same domain, by entering a URL like `http://www.${dom}/squirrelmail/`.