strange errorcode

[Van Liedekerke Franky]

Hi,

sometimes when people from the internet sent mail to one of my clients, they
get the following back from their emailserver (in this case
xs02-078.support.nl [195.114.229.78])

> 451 <[EMAIL PROTECTED]>... I/O error: Error 0
> 
Now I know this is not a qmail error message, but does anybody know why they
get this error? Is the problem located on my mailserver or on the remote
side?

Franky