Choose a level (FATAL, ERROR, WARN, INFO, DEBUG, ANY) if you want to specify a level of email alert to send a message without a waiting period.
Recommendation: Send email immediately for ERROR
Note:
Send email immediately..., Max alerts per email, and Timeout work together: An email with the pending alerts is sent out whenever any of the three criteria is met.
If you would like to be notified quickly, choose a low timeout not a low number of alerts per email. Use the number of alerts per email to keep emails to a reasonable size. Setting it too low has the potential of degrading system performance in case of a surge in alert frequency. Similarly, choosing a trigger level in the Send email immediately field at or below INFO can cause a flood of email messages and slow down the system.