We updated a nameserver for one of our clients domains only to find out later that he already had mails set up a different nameserver (the one we were asked to replace).
For the period it was changed, his mails were getting routed to our DNS which did not have an MX record in it. Is there any way of recovering mails that were sent during this time? What will his recipients have seen?
Will there be a log anywhere of these mails?