If you see an error like this while trying to send an email via your Exchange server
E32F1291C 5322 Tue Aug 26 09:15:08 MAILER-DAEMON (host yourexchangeserver.com[10.10.10.10] said: 452 4.3.1 Insufficient system resources (in reply to MAIL FROM command))
then the system partition of the Exchange server has become low on free space. I have been watching this, if the free space on the drive C: of my server becomes less then 6% of the whole partition size. These are still more than 3 GByte!
You don’t need to do anything on the Exchange server but to free some additional space.