It's likely you've assigned the Web Hostname to a domain which is not bound (In Settings>>Setup>>System Configuration).
It’s best to leave the Web Hostname blank until you know your machines IP address. Blank = bind to all available interfaces.
Since you won't be able to access the GUI to change this, you’ll need to access the database and change it manually.
In Windows, one way to do this is download the free SQLite Expert Personal software from http://www.sqliteexpert.com/download.html then install it, and find the mwes.db file in C:\Program Files\MailWasher Enterprise Server\data, navigate to the configure table and change the web_hostname to blank.
Restart the Mailwasher Enterprise Server Service, and then you should be able to access the GUI.