if the field is blank more than 10 days of record creation in Salesforce, we need to send a mail.

Hi Pavan,

As per my understanding,  you will need to write an Apex Batch and schedule it to run every day at 12:00 AM (i.e. midnight). In the Start method of the batch class, you will have to fetch all the all the records that have a blank value in the field you need to check and Event Start Date - Days in Advance to send email notification is equal to Today. Now, since you have all the records fulfilling your criteria, you can write the logic to send email in the Execute or Finish (if you need to perform some operation before sending mail) method of the batch.

Hope this helps.

Thanks,
Subhendu