To setup your iOS Device, you will need the incoming server information provided by your forwarding address.
For example, if you use Gmail, you will need their POP/IMAP settings. Once you have your incoming server settings on hand, you can begin setting up Mail for your Pobox account.
Setting this up will allow you to send messages through our SMTP, with your From address being your @pobox.com address, or your personal domain address, if you set one up for your account.
First, navigate over to your Settings. When viewing settings, scroll to Passwords & Accounts:
Then, select the option Add Account. At the bottom of the screen, choose Other:
Next, select Add Mail Account:
The Outgoing Server settings should be:
When finished, press Next in the top right hand corner. If all of the settings are correct, the page will change and show the following:
Notes do not sync with a Pobox account, so leaving it on or off will not affect mail. To finish, press Save in the top right corner!