This works in iOS 9.01. Here it is, screen by screen, exactly as you will see it.
1. Go to Settings
2. Then select "Mails, Contacts,and Calendars"
3. Add account
4. Select "Other" and select "Add Mail Account"
Name: Your Name
Email: Your business email address: name@yourdomain.com
Password: password for your business email
Description: will autofill from your business domain
5. Select "Next"
6. It defaults to IMAP at the top of the screen – the bar is blue – but you can also select POP. The following is for IMAP only.
INCOMING MAIL SERVER
Host Name: imap.mail.yahoo.com
User name: Your business email address: name@yourdomain.com
Password: password for your business email
OUTGOING MAIL SERVER
Host Name: smtp.mail.yahoo.com
User name: Your business email address: name@yourdomain.com
Password: password for your business email
7. Select "Next"
8. Slide Mail and Notes to ON
9. Save
When you check email, nothing will display till you go to your Mailboxes and select one or more.