May I refer you to my letter of 14 May?
What does this sentence mean?

Doe this mean "May I post you my letter?"?
It means: Please read the letter that I sent you on the 14 May. (The letter was dated 14 May.)
No it means please look at the letter on the 14th of May.

I hope that helps:)
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 AlpheccaStars's reply was promoted to an answer.