If you receive this error when trying to send email, it will be followed by some numbers – a fraction and a percentage. e.g. ((5/5) 100%)
The message indicates that recent messages sent from your account were bounced by the recipient email address. A large number of bounced emails is often a sign of spam being sent, as such above a certain threshold your ability to send email is temporarily suspended to protect your account.
The block will time out within an hour and you’ll be able to send again – however, if you’ve not been knowingly sending any emails it’s well worth checking your mail delivery report in your control panel by visiting the ‘Track Delivery’ option.
In the event you see emails you haven’t sent, you should change the mailbox password to protect your email.