451 4.3.5 Server configuration problem

It turns out that in these days the mail was working well, I let them send without any problem and everything was perfect. But one day (Today) I was entering the Webmail and I got the message saying “Can not no sent message”. I thought it was just from there and decided to open the Outlook to verify that it was not that but I was surprised that when using the Outlook I said “451 4.3.5 Server configuration problem” or rather.

"The task ‘Sending sender@mail.net’ reported the error (0x800CCC6A): 'The outgoing mail server (SMTP) has encountered an internal error. If you continue to receive this message, please contact the server administrator or the server. Internet Service Provider (ISP) The server replied: 451 4.3.5 Server configuration problem ', but the worst thing is that it was working from 10 when I installed it.

You made any changes to postfix configuration files?

None, all are original as they should be in the factory. That’s why I see it very strange.