Is there an autorespond email function for profile form sign ups (wordpress)?
Third option is to use the CiviCRM extension CiviRules. It allows you to set up a rule (in this case when contact is added to group), a condition (group is xxxx) and an action (send email). You will have to add the send email to a specific address option (or wait for someone else to sponsor this action development as there is already a GitHub issue for it). 
More information on http://redmine.civicoop.org/projects/civirules/wiki and you can get the extension from https://github.com/CiviCooP/org.civicoop.civirules

The CiviRules extension is now live at MAF Norge and will be tested by Amnesty International Flanders.