If the gateway not set up then you will get a message like :
Failed to send e-mail to larry@oracle.com: For e-mail notifications to be sent, your Super Administrator must configure an Outgoing Mail (SMTP) Server within Enterprise Manager. (SYSMAN, myrule)
Invalid host name will give an error like
Failed to connect to gateway: badhost.us.oracle.com: Sending failed;
nested exception is:
javax.mail.MessagingException: Unknown SMTP host: badhost.us.oracle.com;
Invalid e-mail address
Failed to connect to gateway: rgmemeasmtp.oraclecorp.com: Sending failed;
nested exception is:
javax.mail.MessagingException: 550 5.7.1 <smpemailtest_ie@oracle.com>... Access denied
Listening on port other than 25 (bug 3546094) will get a connection refused error
Use the Test button to make sure the e-mail gateway configuration is valid. Check that an e-mail is received at the Sender’s e-mail address