If you find that you are unable to send messages, it may be that we have detected suspicious activity in your account. You may see an error when trying to send an email message: "End-of-data rejected: user has temporarily exceeded the allowed mail recipient relays per day. Please try again later." Or, you may receive multiple emails from "mailer daemon" indicating there was a problem with delivery.
If you believe the error is not related to your email sending behavior or if you see messages sent from your account that you did not send, it's possible somebody else may be using your account to send mail. We advise you to change your password. You should be able to resume sending emails within 24 hours.
Please read our FAQs:
How do I choose a strong password?