These instructions are based on the following link:
http://www.windowsphone.com/en-US/how-to/wp7/people/set-up-an-email-account):
On Start, flick left to the App list, tap Settings Settings icon, and then tap Email + accounts.
Tap Add an account > Other account.
Look for “Advanced Setup” in the email setup area
In Advanced Setup, tap Internet Email Account
Account Name: [a descriptive name for the account like “My Email”]
Your Name: [their full name]
Incoming Email Server: mail.[your domain name] Example: mail.domain.com
Account Type: IMAP4
Username: [Your full email address]
Password: [Your Password]
Outgoing Email Server: mail.[your domain name] Example: mail.domain.com:587 (if it doesn’t work with the “:587” on the end, try :26, if that doesn’t work, remove it)
Outgoing server requires authentication: YES
Use the same username and password for sending email: YES
Verify there are no typos, then tap SIGN-IN