This applies only to those who are attempting or have gone from 4.5.x to 5.0.x, and have LDAP replicas.
-This is in the release notes as well but we want to make doubly sure everyone saw it.
An issue has been identified with LDAP replication during upgrade to 5.0.x. This is due to a bug in OpenLDAP (fixed) that can cause the replica database to become inconsistent when upgrading combined with a tiny bug in the zmldapapplylidf script (also fixed).
For any ZCS 4.5.x upgrading to any version of ZCS 5.0.x, please use the workaround in this article: LDAP Replicas 4.5.x to 5.0.x - Zimbra :: Wiki
This procedure allows all the replica servers to properly preserve the changes made to the master during the upgrade process and allows ZCS 5.0.x non-LDAP servers to work with the 4.5.x replica servers.
Choosing to remove your LDAP replicas during the upgrade and install fresh ones is also an alternative if you wish.
The wiki page also includes directions for those who have already upgraded from 4.5.x to 5.0.x, and have had their replicas become out-of-sync.
Bug 23627 - LDAP replication broken (webapps not working after upgrade)
Bug 23764 - zmldapapplyldif makes modifications to master and replica while replication is not enabled
ZCS Open Source Edition Release Notes
ZCS Network Edition Release Notes can be found in the Support Portal
Once again, if not using LDAP replication you may disregard
UPDATED Information for those running LDAP Replicas:
-We strongly suggest that if you ever did an upgrade from 4.5.10 (or prior) -> 5.0.1 (or prior) at any time and have LDAP replicas, please go & refresh the replicas.
-Updating to 5.0.2 will not fix the data issues in the replicas. The only solution is to reload the replicas if you went from 4.5.10 (or prior) -> 5.0.1 (or prior).
Still in the 4.5.x series?
-If you make use of LDAP replicas & are still on 4.5.10 (or prior) please update to 4.5.11 before switching to 5.0.2
-When they come out, if you have LDAP replicas when going 4.5.11 > 5.0.2 you should still follow the directions given at LDAP Replicas 4.5.x to 5.0.x - Zimbra :: Wiki on updating the replica schemas before upgrading the master LDAP.
-Should you forget to follow these instructions when upgrading from 4.5.11 -> 5.0.2, don't despair! No harm to your ldap data will occur, however some parts of ZCS will not function correctly until all of the replicas are also upgraded to 5.0.2
-From 4.5.11, you will still run into the zimbraAdminURL bug when you take your master to 5.0.2, until all replicas are also on 5.0.2.
You can avoid this by doing the same upgrade procedure we had for going from 4.5.10 (or prior) > 5.0.1 (or prior), where you update zimbra.schema on the replicas prior to upgrading the master.
The big difference between 4.5.10 and 4.5.11 on a v5 upgrade, is that if you choose not to upgrade zimbra.schema prior to upgrading the master, your replica DB will remain consistent with 4.5.11, whereas with 4.5.10 certain changes would not be propagated and the replica databases would be inconsistent from then on.
The procedure allows all the replica servers to properly preserve the changes made to the master during the upgrade process and allows ZCS 5.0.x non-LDAP servers to work with the 4.5.x replica servers.
UPDATE2: You should also follow the instructions to replace the zmupgrade.pm script file on the LDAP replicas in order to avoid the mime tree getting deleted. When it is released, 5.0.3 will have the updated zmupgrade.pm file included.