He sent Kim a congratulatory letter.

他给金写了封祝贺信。

《柯林斯英汉双解大词典》

On November 6, two days after the US election, Ahmadinejad sent a congratulatory letter to Obama.

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For example, when Keynes pivoted to a protectionist stance on trade in 1933, he was mortified to receive a congratulatory letter from Oswald Mosley, who had founded the British Union of Fascists the previous year.

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If you applied for financial aid, you should have received a financial aid award package along with the congratulatory admission letter.

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