Actually youre wrong and you didnt fully understand zimbras structur. While i critise quiet frequently many things in zimbra this isnt zimbras fault.
Zimbras core config is in ldap and update secure.
but it set up on many opensource packages which are different developed with their own config.
zimbra abstract as much as they can but its not possible todo it all.
this sound like a disadvantage but dont forget we profit from several independent opensource projects
with very big potential, i doubt vmware could reproduce what they already have done.
and actually to set dspams score you DO edit sourcecode - its the amavisd perl code you edit
unfortunate that setting isnt in a config its in the code itself
and youre also wrong. no matter which major server (real enterprise) produkt you take upgrades are often quiet a hassel often impossible.
just look at microsoft and upgrade paths, or the forestprep which doenst work as expected most of the times if excahnge is involved.
i could give you quiet a list where you cant even get your config cause its stored in active directory and heres no way of extraction or reaply
also you dont do upgrades daily, and if you do that on such a product you should take at least a day time for preparations.
reading the releasenotes, preparing systems, making backups even testing on a clone - edit 5-8 configs with 2 lines each shouldn be a dealbreaker
is it perfect? no but it wont be ever, postfix will invent new featues, will deprecate old, if you set special customs ones how could zimbra know to upgrade those?
by all negatives in zimbra, even with its off way of storage, but the upgrade is one of the best on an enterprise produkt ever. period.
iam upgrading since early 6er on OSS and NE, i made every step in between, i never had an issue, that in a multinode config together which little custom stuff
so sorry but i really have to strongly disagree here.