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Do the following sentences mean the same?

1: (I'm) sending this email on behalf of John.

2: (I'm) sending this email on the request of John.
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1: (I'm) sending this email on behalf of John. I'm doing that for him.

2: (I'm) sending this email at the request of John.
I'm doing that for him. He asked me to do it.
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I am sending this email to John's request to talk about...
Is that sentence wrong ? If yes, which my mistake you suppose is to ?
I am brazilian. Problem with the latin reference language ?
I am sending this email in response to John's request to talk about...

John has asked me to talk to you about...

Dear Mr Jeffrey,


I’m sending this email on behalf of Mr Teo, with Infinops Pte Ltd 3 years Annual Reports attached.

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