admin emails stopped working

Dont know why but sinces last night i dont receive any emails that i used to get as admin

like

new members registered

the email for cron job status

emails from contact us and so on

what can be happening for this to stop all of a sudden?

I have exactly the same problem. I have cleared the cache and changed the cache settings (as per other post on this site) but everything has dried up.  I was getting a heap of false emails for "possible security attack!" but I changed the security settings and they have since stopped. Did that max out the email sens limits? Does my lack of email mean that my members are also not getting their emails? eg confirm, welcome, etc?