FYI: Email Creation will no long work for Optimum/Suddenlink emails after May 4, 2021. existing emails will continue to work. However after May 4th, new and existing customers won't be able to create any new Optimum or Suddenlink Email Accounts.
How do I reach optimum customer service?
You can reach them by calling 866-209-1099 or by chatting online. If you have questions with your current account, reach out to Customer Service.