For Optimum email settings for iphone, follow the steps mentioned here. First of all, go to your phone's settings and click on "Mail" and select "Accounts" and then you need to go to the "Add Account" option and select the "Add Account" option. After that, you need to select the "Other" option from the available options in the menu. Then, click on the "Add Mail Account" option. Next, enter all the important information such as your email address, and password in the given field boxes, and then press "Next" button. You must choose either from the "POP" or "IMAP" server according to your requirements. Then, you will be asked for the verification of incoming and outgoing server details. Lastly, click on Save to save the Optimum email settings.