Welcome to the forums,
This is a slightly older thread; I'm sorry I cannot tell you if there were server side changes that were made to effect this at the same time (the zimbra employees who develop it may be able to answer that).
Thus, you're supposed to use the connector version that's as close to your server version as possible, but yes there's backwards compatability because you can't immediately upgrade your server & an entire fleet of outlook users at the exact same time.
I would upgrade to
4.5.9 and distribute the newest connector.
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