Our Exchange 5.5 SP4 box is filling the disk to near
capacity, full of .dat files in the MTAData directory.
Most all of the messages sitting in there are spams sent
to non-existent mailboxes at our domain. As I understand
it, Exchange 5.5 is not fully RFC compliant, in that it
will accept email for a domain without first checking for
undeliverable when it realizes there is no mailbox
configured for that user. It appears now that the server
is letting these messages sit queued up waiting for
delivery to a box which never happens, not trying to
bounce them, so the MTAData directory just fills until the
disk has no more space.
Any ideas what might be wrong, or is there any way to
force the server to perform a valid-recipient check before
accepting mail? Spam is collecting in this directory at
the rate of several gigs per week, so it's a very serious
problem for us.