geezz.. first the dev server's sata harddisk gives up, and when we finish replacing and reinstalling debian, then mail server's motherboard goes dead.. this was yet another test case for murphy's law..
when things have to go bad, they will, and at the worst possible time 
After all this turmoil, we have ordered a new server. An
HP Proliant ML350 , complete with dual xeon processors, 4 GiB ECC RAM and SCSI harddisks in RAID1. It should get delivered by this friday it seems.