I am working on a project in which i need to send emails after 3 days of adding projects .is it possible using php?

You can make a script that does that in PHP, and use a scheduler to run it on a daily basis.

You can make a script that does that in PHP, and use a scheduler to run it on a daily basis.

how it is possible?

It can but you have to think of algorithms and the conditions

Place the info you want to send in the Database. and date you want to send it on.

In Linux you have a cron, which you can schedual to run every minute. Write a code that checks if there is something in the Db so send, if so send it and updates the Db that this mail has been sent

I would use cron jobs to run my scripts. You would need to put condition in scripts based on the $date + 3 days to send notification.