Please check this link for setting up alert from OEM:

http://www.oracle.com/technetwork/oem/grid-control/bestpractices-notifications-130521.pdf

I tried this setup but I dont get any notificAtion, my mail server settings work

Have you written the rules for when user account expires then alert ?

Personally I would just write my own procedure to have the database email me.

You can get the expiration date from dba_users and use UTL_MAIL.  Then just schedule it using DBMS_SCHEDULER or DBMS_JOB.

All this is talked about in the docs.

As slightwv said you can also do that, please refer the below link which may help you:

http://download.oracle.com/docs/cd/B28359_01/server.111/b31222/cfrulset.htm

can you pls let me know how to schedule it with DBMS_SCHEDULER or DBMS_JOB

Are you wanting more of real-time alerting that is discussed in the links provided by pinkuray
or
are you wanting something like a daily report?

I would like to get a report daily indicating which oracle accounts which  are going to expire

I should add:
you can write whatever select statement gets you the results you need then apply the answers to all your other questions related to this topic to actually get the email and get it scheduled.

We cannot answer that here until you decide on an architecture for the process.

Like I mentioned in your other questions:
I would create a stored procedure that generates the 'list' you want.  Store that list in a varchar2 variable (remember the 32K limit), use UTL_MAIL to send it.  Then use DBMS_JOB or DBMS_SCHEDULER to run it every day.

If the 'list' can be greater than 32K then, as mentioned in your other questions, use UTL_SMTP and then you can use a CLOB to store the 'list'.