Email sending status failed for Workflow

Hi everyone!

I have configured E-mail set up and parameters for sending emails to user. For workflow, i want to send notification via E-mail to Approvers Like(Please Approve record etc…). So, after i submit a records, i check email sending status, records are created for Approvers with their mail-id with waiting(0) status. Later, it goes to Failed status. Whats wrong in that?.

I am getting pop up notification.

I have checked with change based alert , its sending emails no problem.

also, when i enable Notification in Workflow design like (Send Message when the status is Approved) also working fine.