Spotlight will treat it as the same.If sending a email alert with the filter string "databasename," you'll get email alerts for both databasename and databasename_ .
If you only want email alert for "databasename":
1. Use your Outlook filter to filter out email with the "databasename_".
2. Create a another Alarm Action with the complete key work "databasename_" and suppress the alarms with that word. If you want to do this, keep in mind two things:
a. When an alarm is suppressed, you will not see it in the Spotlight Home Page.