A profile can be mapped to more than one project, using the Project Mappings as previously described. If there is more than one project mapped then you can use rules to direct the emails to the correct project. If there is only one project mapped, then you will not be able to add a new rule, because the default settings will always apply.
If you have more than one project mapped you can access rules, but clicking on Rules on the right of your screen, then click on Create to add a new rule
This will bring up a create box similar to the following
Syntax help for using regexes are described on this page.
After you have filled in the fields, click on Submit to save your changes.