User to user email not working?

[stained]

I'm using the php standard email settings and have been testing user to user email in response to a query from one of my members. I've sent a few test emails between a couple of accounts set up for the test and none of the messages has come through to the respective email accounts(I've waited an hour so far and still nothing). Do I need to set up user to user email seperately? Admin emails come through fine.