Upon checking the Mail Tracking Logs, it was found that the emails are getting quarantined due to the High-Risk Attachment policy. The policy has a rule wherein if the number of attachments is greater than 20, the email will be quarantined.

To resolve the issue, the number of attachments in the email should be reduced to less than 20. In case it is required to send an email with more than 20 attachments, the policy rule can be modified accordingly to allow it. However, it is advisable to avoid sending such emails with a large number of attachments as they may be flagged as spam or high risk.