I have a drop down column which has numbers from 1 to 30. customer selects any of the numbers the mail should trigger. Lets say today Aug 01st and selected 10 from drop down column, the mail should trigger on Aug 11th. if selected 3, mail to be triggered on Aug 04th and so on. How can i achieve this. please guide me.
Using SPD workflow.. you can be able to check the selected field value and even send mail to the customer. But the issue here is, a workflow is invoked at the time of any modification to the list item.
As In your case you need to send the mail the very next day. So out of the box using SPD is not possible.. You can write a timer job which can check the date and send the mail as your requirement.
You can pause a WorkFlow for a certain duration. Invoke your workflow when an item is updated then pause your workflow for 1 day and then e-mail will be sent the next day automatically.
Here is some details for pausing workflow: Reference Guide