The Monitoring and Alerting Infrastructure (MAI) in SAP Solution Manager provides the enhancement spot ALERT_REACTION where you can specify custom alert reactions.
This enhancement spot and the corresponding Business Add-In (BAdI) BADI_ALERT_REACTION are described in the document MAI-Alert-Consumer-BAdI-Interface.zip.

This functionality can be used to trigger additional events in case of an alert like for example:

• Calling an external web service on a 3rd party incident management tool
• Write information to a log file
• Send SNMP trap to third party tool. 
  A standard implementation of this functionality is available with SAP Solution Manager (see document HOW-TO GUIDE-SNMP-Trap-Adapter.pdf below).
• Execute additional OS commands on the SAP Solution Manager. 
  A standard implementation of this functionality is available with SAP Solution Manager (see document HOW-TO-GUIDE-OS-Command-Adapter.pdf).

Customizing Email Notifications

There is also a BAdI interface which allows you to change the content of an email notification before it is sent. This interface is described in the SAP Note 1747633(opens in new tab).