Contratulations,fella.I heard you'll be promoted.
恭喜啊老兄，听说你要升职了。
You are kidding me.
你在开我的玩笑吧。
No,I'm not.I got the tip straight from the horse's mouth.
没有，我不是开玩笑，这个消息千真万确。

I got the tip straight from the horse's mouth.You are going to transfer to the marketing team.
我收到准确消息，你要被转到市场部啦！
No way.I'm so excited.
不会吧。我好激动啊！

精讲部分

This is absolutely true.
I got the tip straight from the horse's mouth.
straight from the horse's mouth常用来形容“消息绝对可靠”。据说，马的乳门齿，乳中齿会随着年岁的增长被永久门齿，永久中齿依次顶落，而且马的切齿由于进食也会受到磨损，所以有经验的驯马师常通过马的牙齿来获知马的年龄。日常生活中，straight from the horse's mouth更常用来形容“消息等直接来自当事人”，表示绝对可靠。Tip原指关于赛马的内部消息，引申为“内部情报，秘密消息”。