求翻译：关于第321号1000箱蘑菇罐头的售货合约，兹通知你方，我们已由伦敦中国银行开立了第853号保兑的，不可撤销的信用证，计金额10000英镑，有效期至7月15日止。是什么意思？

No. 321 of 1000 boxes of canned mushrooms, Sales Contract, hereby inform you, 853 confirmed, irrevocable letter of credit opened by the London Bank of China, the total amount of £ 10,000 is valid until July 15 date.

In 1000 chassis No. 321 canned mushrooms contract for the sale, I wish to inform you that we have the London Bank of China set up a 853 number, confirming the irrevocable letter of credit amount, £10,000 and is valid until 15 July.

About the 321st 1000 box of mushroom canned food vending contract, this informs you, we to draw up 853rd by London Bank of China to guarantee cashing, cannot be abolished the letter of credit, counts the amount 10000 pounds, stops the term of validity to July 15.

No. 321 1000 boxes of canned mushrooms, sales contracts, we hereby inform you, we have confirmed, by the London Bank of China opened No. 853, irrevocable letters of credit, including the amount of 10,000 pounds, valid until July 15.

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