1. Select the Settings Icon from your iPhone home screen.
2. Select Accounts & Passwords.
3. Select Add Account...
4. Select Other
5. Select Add Mail Account
6. Type in your email address and password and description.
7. Select IMAP, then fill in your email address & password and the server information for INCOMING / OUTGOING SETTINGS.
You need to complete all fields.
8. When attempting to verify you "may" receive the message "Cannot Connect Using SSL - Do you want to try setting up the account without SSL?" If you do, then select YES. After a few seconds you will receive the exact same message, select YES again. After the 2nd time you will get all check marks and you'll see the following image.
9. Mail should be set to ON and Notes should be set to OFF, Select Save
10. Congratulations you have successfully setup your mailbox to use IMAP on your iPhone.
CONTINUE TO SETUP ADVANCED SETTINGS BELOW
11. From your iPhone Home Screen, Go to Settings > Mail, Contacts, and Calendars > Select the Account in Question > Select your Account
12. Under Outgoing Mail Server, Select SMTP
13. Confirm the Primary Server is ON, Select the Primary Server
14. Confirm you've completed the Host Name, User Name, and Password fields. Confirm Use SSL is OFF. Change Authentication to PASSWORD. Confirm Server Port is set to 587. Select DONE, Select Account (top left)
15. Select Advanced
16. Under Incoming Settings, Confirm you've completed the Host Name, User Name, and Password fields. Confirm Use SSL is OFF. Change Authentication to PASSWORD. Confirm Server Port is set to 143.
17. So you don't take up mailbox space on the mail server you can edit your Mailbox Behaviors so that either Drafts, Sent, or Deleted messages are stored on your iPhone. Select Select Drafts Mailbox
18. Confirm you have selected Drafts under On My iPhone.
19. Repeat Step #17 and #18 for the Sent Mailbox & Deleted mailbox