Email alerts?

My email alert on Messenger is not working. I've already gone into preferences and everything is correct. I'm also not getting the envelope email icon on my taskbar either. Nor is my Mail tab updating on my yahoo toolbar. I could have 5 messages and it doesn't say anything on it, and without the alert chiming me or the envelope poppin out, or even my right hand bottom corner alert is not working. What do I do?