You need to configure the outgoing mail settings in the following way:
Outgoing Mail server
Host Name mail1.eircom.net
User Name Optional
Use SSL OFF
Authentication > Password
Server Port 587
Make sure you do not fill in the username and password sections, they will simply say 'optional'
Then press done and Eircom will verify settings completing the set up of your account.
This took me ages to work out and neither O2, Eircom nor Apple were much help. I finally found a solution at Boards.ie
Hope this helps.