The 'Check Presence in NAB' option checks if an ACL entry is present in the NAB.
When enabled, this feature will display red cells to indicate that those entries were NOT found in the current Domino Names and Address Book.
In addition, a flag will mark these entries in the 'Is in NAB' Column. Grouping by this column will therefore display ALL these invalid ACL Entries and/or users on your server at once.
If the "Check Presence in NAB" feature is enabled, all ACL Entries (displayed in the Name column) and actual resolved user records (displayed in the Members column if Nested groups are expanded) are checked for their presence in the NAB.
Please note that the "Check Presence in NAB" option is enabled by default. If you have a large NAB and a poor connection, the NAB Checker process may stall your system.