Thank you very much ( very, very much) (ever so much) (most sincerely) (indeed) (from the bottom of my heart).
很（非常）（非常非常）（最真诚地）（确实）（衷心）感谢您。

Many thanks for your kind and warm letter.
感谢您友好而热情的来信。

Thanks a million (ever so much).
万分（非常）感谢。

Please accept ( I wish to express )my sincere (grateful) (profound) appreciation for ...
请接受（致以）真挚的（衷心的）（深切的）感谢……

I sincerely (deeply) (warmly) appreciate ...
我真挚的（深深的）（热情的）感谢……

I am very sincerely (most) (truly) grateful to you for ...
为了……，我非常真挚的（深深的）（真诚的）感谢您。

There is nothing more important (satisfying) (gratifying) to me than to receive one of your letters.
再也没有比收到您的来信更使我觉得重要（快慰）（感激）了。

Your letters are so much fun (comfort) (entertainment) (company).
您的来信充满了乐趣（给了很大安慰）（带来了欢乐）（使我不感寂寞）。

Your most courteous (considerate)(delightful)letter...
您那彬彬有礼（体贴入微）（令人欣慰）的来信……

I cannot tell you how much your letter delighted(relieved)(amused)(enchanted)me.
我无法告诉您，您的来信使我多么高兴（宽慰）（觉得有趣）（陶醉）。

I love the way you say (put) things in your letters. You make even the smallest incident seem so interesting(important)(charming)(mysterious).
我很欣赏您在信中描述各种事物的手法。您的妙笔使细小的事情都显得很有趣（重要）（动人）（神秘）。

It was good (fine)(charming)(thoughtful)of you...
承蒙好意（美意）（盛情）（关心）……

It was nice(characteristically thoughtful) (more than kind) of you...
承蒙好意（特别关心）（十二分好意）……

At the outset, I want to thank you for your kindness to me and for your compliments.
首先，我要感谢您对我的友爱和问候。

Believe me, I am truly grateful for...
我确实真诚地感谢你……

We were deeply touched by ...
……使我们深受感动。

It is a hopeless(definite)(positive)understatement to say that I am deeply (sincerely)(truly)grateful.
这就是说“我深深的（真挚的）（真诚的）感谢”远不足以（不能确切）（不能明确）表达我的谢意。

It‘s generous of you to take so much interest in my work( to give me so much of your time) (to show me so much consideration).
承蒙对我的工作如此操心（为我花费这么多时间）（对我如此关怀）。

We are indebted to you...
我们感谢你……

I regret very much that I did not have an opportunity to thank you personally for ...
未能面谢，深表遗憾。