Before anything else supposse that your domain is midominio123.com and that the email account you whish to configure is firstname.lastname@example.org.
Note that you can follow this guide to configure any iOS device ( iPhone or iPad ) from version from 7.0 to 8.3, as the process is almost identifical.
1 - Add account
First step is to open your phone's Settings, then scroll down and click on Mails, Contacts, Calendars. Once there click on Add Mail Account and finally select Other.
2 - Write your name, email and password
Write your full name, email address you wish to configure and it's password. Then click Next.
3 - Incoming and Outgoing mail server
Fill in all empty fields on Incoming and Outgoing mail server sections. Then click Next. The device will try to verify settings.
4 - Cannot verify server identity
While verifying it may show you a warning saying something like "Cannot verify server identity". Just click on Continue.
5 - It's done
Finally it will allow you to choose the apps you wish to use with the newly configured account. Click on Save and then open the Mail.