The following article explains how you can configure your webmail on iphone. To do that please follow these steps:
1) From the Dashboard, Click "setting".
2) Under settings, select "Mail".
3) Select "Add Accpunt".
4) Select Other as the type of account.
5) Select IMAP.
6) Enter the requested Information
Name: the name of the mail user
Address: the email address of the mail user.
Description: a description of the mail user.
Host Name: enter the mail server "mail.yourdomain.com" (Incoming mail server and external mail server).
Username: enter the full email address ( incoming mail server and external mail server).
Password: enter the users password (incoming mail server and external mail server).
7) Click Save.
8) If you see a message that says " cannot connect using SSL", click "Yes" when asked to setup the account without SSL..
9) Click Save.
10) Click settings for the account you just created.
11) Click Advanced.
12) Set Incoming uses SSL and Outgoing uses SSL is OFF.
13) Under incoming settings, click Authentication and select Password.
14) Under Outgoing settings, click Authentication and select Password.