Problem
You receive a notification about an alert being created for a SharePoint List but receive no actual alerts after that.
Cause
Alerts not being received can be caused by so many things but one of the possible causes is your antivirus software on the SharePoint Server.
Our antivirus software has port blocking rules to prevent mass emailing by malicious programs and it needs to be configured to exclude SharePoint from this rule.
Solution
Configure the OWSTIMER.EXE (SharePoint's Timer Process) to allow to send emails in your antivirus software.