attestation policy not sending mails

Hello Team,

I set-up a new Attestation policy and triggered Attestation manually for few accounts.

Attestations are available for approving in web portal but mails are not delivered to approvers enen-though mail template is defined in workflow.

Mail preview is working without any issues

How can we further troubleshoot the issue.

Approver is active in tool and having active mail address/mailbox.