The Mac OS X Server 10.6.5 update is back online, now marked v1.1 and with an incremented build number. It's available through Software Update and for download after fixing a memory aliasing issue in Dovecot's handling of user names.
We reported earlier that the 10.6.5 Server update was pulled briefly, coincident with reports of a number of issues. These included problems with Whole Disk Encryption, DNS resolution issues, LDAP/Open Directory master hiccups and remote connection drops.
It's not clear yet whether the revised update is only associated with the reported security issue, or if it's going to address the other problems reported. Our advice: Wait a few days before applying, use a non-production server to test, and back up first.