Can't send emails - all platforms

[#1]

I'm getting SMTP 452 errors on all my accounts and on Webmail and clients.

Is this just me or is there a wider problem?

I should add that this started yesterday on accounts that were previously working OK

[#2]

Further to the above, it appear that only certain email identities are afftected.  The error received is

'SMTP 452 error -  failed to set sender'

If I change the identity to a fictional address, it works OK

[#3]

I'm getting the same on my exchange server using relay.pndsl.co.uk. On a few email recipients it showing as "452 ... Temporary Failure"

[#4]

All appears to be working again  - for now at least