Where possible, we recommend that you do not signup using a 'personal' email address such as email@example.com. Instead, we recommend you use a generic email address such as firstname.lastname@example.org.
The reason for this is that main admin account cannot be used to administer an employee file so when the main administrator wants to use self service and request holiday and so on they need to use an email address for their login and if their email@example.com account is already in use then it cannot be used again.
It is possible for us to change the admin email address for you so all is not lost. But it is best to use a non-personal email address where possible.