Not sure anyone would know but am interested in other .edu's thoughts: Zimbra can authenticate against a Sun Directory, what keeps it from supporting Sun Directory as its main LDAP store? Is the structure of Zimbra's schema (or objects) incompatible with Sun Directory? If not, what other factors make Sun Directory unsupportable/impossible with Zimbra (is it wanting to have the whole thing OSS, licensing, ..)? What is likelihood for Zimbra to support Solaris? I ask because I'm guessing we're not alone in having significant infrastructure built around Sun Directory and Solaris Sparc. Adopting Zimbra (for us) would be a much easier prospect if Sun Directory, Solaris, or ideally both, were supported.
Dropping my Zimbra hat for a moment, I would agree with what others have noted -- Zimbra is very much a packaged product. Our scripts for managing LDAP expect the LDAP server to be OpenLDAP. In the future (GnR) this coupling will be only tighter as we drop the slapd.conf method of maintaining OpenLDAP and move to the configuration database.
Other reasons outside of the tightness of integration would in my opinion also be performance and data integrity. I used to run a Sun DS cluster at Stanford University, and we finally had to throw it out because of its lovely tendency to corrupt the database without so much as detecting it, wreaking all sorts of havoc (including replicating corrupt data without a pause). It also scaled very poorly, where we ended up having 6 Sun Solaris DS boxes dedicated purely to mail routing, and looking at adding more all the time as mail traffic rose. Moving to OpenLDAP on Solaris allowed us to drop that number down to 3, and realistically things could survive on fewer without problem. When I departed Stanford, we could still route the entire email load across a single linux server without it breaking a sweat, even though mail traffic had increased substantially (I don't recall the exact amount but I think it had at least tripled).
For those interested, there are some older benchmarks I helped Symas perform at:
<http://www.symas.com/benchmark.shtml>Symas also benchmarked Sun DS outside of what Neil Wilson wrote in his blog, but could not post them due to legal issues in the Sun DS license.
I also suggest Howard Chu's presentation to Scale5x: <http://www.openldap.org/pub/hyc/scale2007.pdf> --Quanah -- Quanah Gibson-Mount Principal Software Engineer Zimbra, Inc -------------------- Zimbra :: the leader in open source messaging and collaboration