My wife has been having a problem sending email. We currently use Google Apps for our domain, and when she sends email, she gets the following message:
5.4.5 Daily sending quota exceeded
This message is supposed appear if an account has sent more than 500 messages, or more than 100 when using a mail client. The problem is that she has only sent 2 messages within last 24 hours.
I have filed a trouble ticket, and have posted a message on thir Google Group. In the mean time, I have set up one of our Godaddy email accounts, to allow her to send outgoing mail.