That you mean a lot to them and they are thankful to know you.
It means they recognise that you were of help to them.
It seems pretty straight forward to me. They are showing gratitude for you and whatever way you've helped them. I wish more people were like this.
It means they recognize that you help them in very good way and do something best than others.
They encourages you to do more better.
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Other people asked questions on various topics, and are still waiting for answer. Would be great if you can take a sec and answer them