Please try the following to triage this:
Stop and restart the Orchestra Hub Service, which is used to queue and send emails. Search for 'Services' on your application server, and it will appear.
Wait five seconds after clicking Stop before you start the service again.
Additionally, this could be caused by an option within Synergy not being ticked.
Then navigate to System Manager.
Select Options and then Common.
Mail settings, and check that the option for Enable Email Sending is ticked.
⚠️Important: If this doesn't work, you will have to contact the support desk and provide them with sufficient information such as batch name, date and time, etc.