Source:
http://www.one.com/en/support/guide/mail/setting-up-mail-on-iphone-ipad-ios
http://support.apple.com/kb/HT4810
If you use a common email provider, your device will load your email settings automatically. If your device doesn’t load these settings and you don’t know them, contact your email provider and ask for this information:
My Email settings
My email address:
My email provider:
Incoming Mail Server Settings
Account type (POP or IMAP): IMAP
Incoming Mail Server: For Incoming Mail Server enter imap.domain.com as Host Name, domain.com being your domain
User Name: Enter your full email address as User Name e.g. name@example.com
Password: Your email password
Incoming server port number: 993
Incoming server supports SSL? (yes or no): On
Outgoing Mail Server Settings
Outgoing mail server: or Outgoing Mail Server enter smtp.domain.com as Host Name.
User name: Enter your full email address as User Name e.g. name@example.com
Password: Your email password
Outgoing server port: In Server Port you should use port 465
Outgoing server supports SSL? (yes or no): On