I am pretty sure this was a false alarm as although the server was down, no one seems to have sent any messages when this was the case, so I do not think that the lack of such messages in our archive account is surprising.

We had a problem over the weekend, probably my fault as our Mercury Log file had been allowed to get rather big.  One result is that messages sent between 17.34 on Friday and 10.11 this morning have not apparently gone and do not appear to be in our Queue directory.  Is there anywhere else they could be? 

 The reason I think the messages were not sent is that our Mercury server has a filtering rule which always forwards evcery message to an account called Archive and there are not outgoing messages  in this acount between Friday at 17.34 and Monday at 10.11 which seems unlikely.

Is the system log complete?  That should give a history of what happened over the w/e.

I don't know its over 900 MB in size and I have not yet managed to open it...