There is no limit set in MacDNS, however, the Mac OS file system limits the number of files opened simultaneously. Each zone file counts to this limit and will also increase the application's RAM requirement by about 2 KB.
The number of files you could have opened varies by Mac OS version.
- System 7.x and Mac OS 8.x -> 348 open files.
- Mac OS 9.x -> 8169 open files.