Holy crap how is this not your number one priority to fix and to alert customers about?  This problem has cost me $30,000 in missing invoice payments because Quickbooks randomly never sent them.  This goes back over a year.  And there is no alert, error or any indication that something went wrong.  Generally, getting paid for my work is WHY I WORK.  If Quickbooks can't handle this most fundamental task, why am I using it??