Nightmare !!! (Mac OS X)

[fab]

I have tried with /etc/hosts but to no avail because the problem is not with the DNS service itself but with the dscache instead.
I have no ISP because I work for a big university so we have (and must use) our DNS servers.
I have not tried with dscacheutil -flushcache in the crontab, but I'm afraid that we should run it every minute because we actually have 3000 users so our mail servers can't staying there in "confusion" and waiting for the next flushcache to occur.
In case it may be of interest for someone, these are the dscache stats on our mailbox server (running ZCS 5.0.18 now):

root@mail1:~# dscacheutil -statistics
Overall Statistics:
    Average Call Time     - 0.001214
    Cache Hits            - 6830933
    Cache Misses          - 358593
    Total External Calls  - 5643716

Statistics by procedure:

             Procedure   Cache Hits   Cache Misses   External Calls
    ------------------   ----------   ------------   --------------
              getpwnam       441528          31450           472978
              getpwuid      2456920           2754          2459674
              getgrnam       277617           2126           279743
              getgrgid        47060             83            47143
         getservbyname       712421           1893            68028
        getprotobyname       101187             94           101281
      getprotobynumber       598339           2672           601011
        getrpcbynumber            1              1                2
              getfsent            0              0               32
          getnetbyaddr           28             84              112
           getaddrinfo            0              0           835291
           getnameinfo       499819         260595           760414
         gethostbyname       794475          10987            17922
         gethostbyaddr            0             84               84
            gethostent            0              1                1