Email server problem?

[cs]

Is there a problem with the SMTP server?

I have been happily sending emails all day up until about 13:40 when every email I sent returns the following:
>>
The following recipient(s) cannot be reached:

      'xxxxx@xxxxx.co.uk' on 15/10/2012 13:41
            Server error: '451 4.3.5 Server configuration problem'
>>

Anyone else?

[Rik]

No problem here, but I've not received it yet which makes me wonder if they've had a spam 'hit'.

[Rik]

 Received after 2 minutes.

[cs]

OK thanks!

I think its back now, well sort of......I just received a test message now (14.31) that I sent at 14.18..

All the other emails I sent in between time seem to have disappeared into the ether