You have many customers to whom you extend your services and not all of them would be a verified contact on your portal. This is because you would not be sending an automatic email notification which guides them to set up an account. During such an instance, you could send out an activation URL manually from the "Customers" tab or inform them to do a password reset and activate their account.
A recommendation would be to create an article with complete details about how the account creation in freshdesk works along with information about performing a password reset from the portal homepage. This article would have to be visible to all users - the visibility can be changed in article properties by clicking on edit within the article.