Configuring web domain names
If you are using single product installation to serve mail accounts on multiple domains, you might want to supply different settings for different domains (e.g. different skin for each domain) and to ensure the settings are obtained correctly when webmail interface is used.
For that, you'll need several different URLs to point to your WebMail installation. The easiest way is to work with subdomains. Let's assume WebMail is used to access mailboxes on maildomain1.com and maildomain2.com domains, and you have those domains added to WebMail.
For your WebMail installation, you'll need 2 subdomains, for instance maildomain1.webmail.com and maildomain2.webmail.com. Set "Web Domain Name" to "maildomain1.webmail" for maildomain1.com domain, and "maildomain2.webmail" for maildomain2.com domain.
Once that's done, navigating to http://maildomain1.webmail.com/ would have the effect of using maildomain1.com configuration settings. Same goes for the rest of domains. If none of web domains match, default domain options apply.