Alert has stopped reporting on events

I have had a few alerts set up for the last couple of months or so, and yesterday I decided to change the mail server sender address to something more meaningful (an address that denoted from which domain the alert was alerting on). This is a Snort alert in particular, and it seemed to work fine after this. So I decided to do another experiment, and remove all "Log Message" search terms to see what the alert would report (since there is no explicit explanation of what this action does). Since I made this change and clicked Save, that alert and others I had created completely STOPPED sending email alerts. The events were still pouring in from the Snort machine, but on the status of the alerts, they were all Failed. The only alert that has sent anything is a Windows alert for my domain controllers, so I know the email server settings are not the issue. Any help would be appreciated!