You must already be a Blackbit customer and have access to https://workmail.blackbit.io to create new accounts.
On https://workmail.blackbit.io Blackbit offers an administration of your WorkMail organization. All mail domains and accounts are assigned to your organization. You can obtain the login on request from Blackbit Support by sending an e-mail to email@example.com. With Blackbit WorkMail you can order a new account independently. To do this, click on the corresponding organization in Blackbit WorkMail and then on + Set up a new account.