Configuring IIS smtp with gmail

Configuring IIS smtp with gmail

I am using Windows Server 2012. I followed following URL for configuring
IIS smtp
http://blogs.technet.com/b/yashgoel-msft/archive/2012/10/26/configuring-outgoing-email-settings-in-sharepoint-with-gmail-smtp.aspx
Now my problem is my email are stuck in queued folder, I feel like as I
have 2-step verification in gmail account is getting reject. So I change
password in my smtp to application specific password. But still same
problem.
So now I wanted to know what can be the problem. Is there any tool from
which we can say that smtp of gmail is rejecting email.
Hope somebody can help me over here