Perhaps this is the reason that I have been getting error messages from our software.
For about the last three weeks I have been getting message that our software had attempted to send you an email to notify you of a new post to a thread you are subscribed to but could not for some reason.

I did not notify you personally because you were not the only member that this was happening to. I knew it was not the fault of our forum software so there was nothing that could be done on this end.