Hi Luca, unfortunately if the emails failed being written to disk due to space they may be lost at this point. Do you have an incoming gateway of any kind that might be capable of resending them perhaps? Alternatively you might also find them in your Message Archive if you have this functionality enabled for that domain. Those EMLs are usually kept in C:\SmarterMail\Archive if enabled. I hope that helps!
Kyle Kerst
System/Network Administrator
SmarterTools Inc.
www.smartertools.com