Read this to know how you can configure your iPhone with your Optimum email account.
Go to the settings in your iPhone then choose Mail, contacts, and calendars. Choose Add Accounts and tap on others.
Choose to Add mail accounts and enter your name, optimum email ID, and password then click next.
Enter incoming and outgoing mail server details in required fields and tap save. Congratulation now your optimum email account configuration in your iPhone is completed.
If not then you can call on the Optimum email customer support number for more help.