Hi Swapna. It is not clear what you mean by "from past few days I started seeing even the data alert condition appearing in the email." Do you mean that you are not receiving the emails that you would expect to, based on the way your alerts are configured?
If so, you can test whether the SMTP settings are correct by setting up a standard subscription on any viz, and then waiting to see if you receive it. Be sure to check your Spam folder and any filters you may have set up on your email client--many times these emails get filtered, and people are not aware of it.
Your server / site administrator can also check the Background Tasks for Non-Extracts admin view and see if there are any failures.