this is not stored in the nas databases.
You could look for the email action but this will probably not provide you with what you are looking for as this only provides that a NIMBUS message with an email subject was sent.
Nothing really about what happened after that.
The only way to see the relationship between a particular alarm and the actual email would be to capture the information from the emailgtw probe logs on loglevel 3 or higher.
there you can see the alarmid along with the information about the sender etc and if the email was successful.
None of this detail is relayed back to the nas probe or stored any place.