To check the non-delivery of emails, verify the following :

1. Navigate to the processed emails section of the Mail Agent. Verify the status of the emails sent. 
   
1. If the status is soft bounce, it could be due to temporary issues. This will usually be resolved in a while and email will be delivered. In some cases, after multiple retries, the soft bounce will become a hard bounce. 
   
2. Hard bounces are caused in cases where the email address is non-reachable. Email addresses causing a hard bounce should be added to the suppression list to avoid bounces.
2. If the status is "Delivered" and the email has not yet been delivered, copy the email's header and drop us a mail at support@zeptomail.com