If you are a new user, then it may not work, or there may be no option for sending the test mail. You may send test mail after verifying the information. please visit Gmail Support USA for more information.
As per: http://docs.splunk.com/Documentation/Splunk/latest/Alert/Emailnotification
You can send email notifications directly from the sendemail search command. Here is an example:
index=main | head 5 | sendemail to= server= subject="Here is an email notification" message="This is an example message" sendresults=true inline=true format=raw sendpdf=true
index=_internal | head 1 | sendemail to="name@my.email.domain" format="html" server=smtp.gmail.com:587 use_tls=1
Until Splunk developers add a "test email" link on the email configuration page, here's a quick way to test your email settings in Splunk.
From the default "Search" home page (the "live dashboard") in version 5.X and earlier, just above the search bar is the "Actions" drop-down menu. Under there choose the "Schedule PDF Delivery..." option. Fill in the "Deliver To" field with your address, then click the "Send Test Email" link at the bottom of that window. Click "Cancel" to exit this window.
In version 6.X I couldn't find the same actions option, but you should be able to use the "sendmail" search command:
* | top 5 host | sendemail to="YourAccount@example.com"
But in my test system this wasn't actually sending an email, even when I added the server= fields to point to my MTA.
There isn't. I filed an enhancement request more than a year ago on this.
I tested my email notification by creating a small schedule search with alert condition of always that sends email.