NetScaler MAS does not send emails when traps are generated on NetScaler.

Verify if those events are captured in NetScaler MAS event logs. We cannot see them in CLI logs as they are directly recorded to the database. If yes, then verify if connection to mail server is taking place. You might see errors similar to the following in mps_event.log file:

Monday, 23 Jan 17 13:42:03.781 +0000 [Error] [Main] Exception : Host not found: mail.citrite.net occurred  while sending mail for rule: email_rule_test

A successful email sending process will be like this:
Thursday, 30 Mar 17 12:45:54.728 +0530 [Debug] [Main] Establising session
Thursday, 30 Mar 17 12:45:55.003 +0530 [Debug] [Main] trying login
Thursday, 30 Mar 17 12:45:55.553 +0530 [Debug] [Main] sending message
Thursday, 30 Mar 17 12:45:57.411 +0530 [Debug] [Main] closing session
Thursday, 30 Mar 17 12:45:57.686 +0530 [Debug] [Main] Updating the database

Over here, you can see NetScaler MAS setting up a session with the email server.

Problem Cause

NetScaler MAS could not locate\connect to the email server.

Citrix Documentation - How to Create Thresholds and Alerts Using NetScaler MAS