I know that the response from oxygen8 was meant well, however, since I speak NO German, it was of little use to me.
I tried swapping out the troublesome LS421DE unit with another (slightly older) unit and with the same settings as the original one, got the same results - While the unit indicated that the test e-mail was successful, NO e-mail was ever received.
I tried changing the IP address of the unit and got the test e-mail, so I restored the original LS421DE with the original settings - Same results, NO e-mail received - Changed IP address down by 1 (xxx.xxx.x.31 to xxx.xxx.x.30) and Got the e-mail!
Sitting on my system for one day, the scheduled e-mail reports ALL came through fine!
I will be re-booting ALL of my LS421DE units (3 each) and All of my LS441DE units (3 each) just to keep them all in sync for future reference.
One final note: While I have had decent results using the Buffalo LS units, my latest unit, a NetGear ReadyNAS 214 with 4 6TB HDD units will ultimately replace the Buffalo units.