Load balancing outgoing mail relay

[freebsd]

>This (multiple A records) works for me, at least approximately. Both
>Bind and MS DNS will round robin when multiple A records exist for the
>same hostname. What is your setup?

FreeBSD 6.2 with Sendmail (initially) and now postfix.
MS DNS with round robin (and TTL set to 0 on the records).
Resolving with nslookup gives something like:
smarthost.domain.tld
192.168.0.1, 192.168.0.2, 192.168.0.3

If I kill 192.168.0.1 then it goes on the second one. But this is failover, 
and I need (approximately) load balancing.
I understand this is related to the MTA and not to the OS, but hopefully 
someone solved this problem using Sendmail or Postifx that are both used on 
FreeBSD.
Thanks