JET errors we get in Exchange, in order of excitement !
Error -1012 - JET_errOutOfDatabaseSpace
Maximum database size reached.. In 5.5/2k/2k3 standard edition, a paultry 16 Gb never went far. With the release of SP2 for Exchange 2003 though this has been ramped up to 75 Gb so we should not see this again.
Error -1018 - JET_errReadVerifyFailure
Checksum error on a database page. Rather vague but possible hardware fault in most cases.
Error -1019 - JET_errPageNotInitialized
Blank database page. There used to be data there, but not now.
Error -1020 - JET_errOutOfFileHandles
When exchange tried to use the database, windows thought it had various files open already and wouldn't give up any more. Bad windows...
Error -1022 - JET_errDiskIO
The disk IO error is rare but if it does rear its ugly head, it's very hardware'y and not exchange.