UID Different Than Mailbox Name

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Can the uid be different than the mailbox name?

This is not supported and will not work in general. You're depending on the LDAP server returning multiple UID attributes in a specific order every time, and there is no guarantee in LDAP that this ordering will be preserved. Sun's LDAP server tends to return attribute values in the same order as long as nothing changes, but setting an unrelated attribute, or backing up and restoring the directory database, or any other activity that perturbs the user entry in some way could change the ordering.

Additionally, while Messaging Server 6.1 doesn't perform a check to insure that there's only a single attribute value with the semantics of a UID on a user entry, in Messaging Server 6.2 there is a check to make sure there's only a single atttribute of this type. Messaging Server 6.3 checks to make sure there's only a single value. So sooner or later an upgrade is going to break this sort of setup.