Re: Can't send emails

I have exactly the same message
An unknown error has occurred. Subject '', Account: '',
Server: '', Protocol: SMTP, Server Response: '451 4.7.1
<END-OF-MESSAGE>: End-of-data rejected: ip has temporarily exceeded the
allowed mail recipient relays per day', Port: 25, Secure(SSL): No,
Server Error: 451, Error Number: 0x800CCC6A
I have not sent any emails this morning so I don't understand.
Any ideas anyone