out of office autoreply

I want to autorespond only to the good messages that reach my Inbox after SpamSieve filtering to let the sender know that I’m not in the office. How do I do that?

Put your auto-respond rule below the SpamSieve rule(s).

So I set up a rule that applies to “Every Message,” set the action to “Reply to Message,” and put that rule directly under the SpamSieve rule? The only ones who will get that reply is the sender any message that gets filter to the Inbox?

Will all those messages that are replied to stay in the Inbox until I return?

Right.

The replies will go to the senders who sent you messages that SpamSieve analyzed and thought were not spam.

That would depend on whether you have any rules below the replying rule that move the messages to other mailboxes.