The first thing you have to do to create a Gmail account is to create first a user account. So you have to go to create user package if you don't have to use our package created you just can use any of them because the package are the conditions that the email account is going to have.
After that you have to create a new user so you say add new user and then you fill all the fields username email password the main user package
When you have a user created you can go to list users and there you will have the user and there in the right part you can login as that user.
Then go to email manager and create an email account. When you go to email accounts you will see that you have for default email account that is created with the user but you can create more if you want.
Set the dns to mxroute: