During SYNC, the SNF node gets status information about its rulebase file. If the file on the server is newer than the one that is active in the SNF engine then a flag is set, the semaphore file is created or overwritten with the timestamp of the newest file, and the update script is run if it is enabled and has not been run within the guard time (3 minutes by default).

The new rulebase is usually detected within about a second of seeing the new file.  The new rulebase will be loaded and checked the new rulebase. If there is something wrong with the rulebase file it will keep the current rulebase active until a better one shows up.

Update notification emails are not needed for the new update mechanism, but they are still an option.