I was delighted/glad to receive your letter. 很高兴收到你的来信。
Your letter came to me this morning. 我今天早上收到了你的来信。
I have received your letter of June the 29th. 我收到了你于6月29日的来信。
How nice to hear from you again. 很高兴再次收到你的来信。
How is it going?最近怎么样?
You asked me about(problem，question...)，now let me give you some advice. 你在来信中询问我……，现在，让我给你一些建议。
It has been a long time since we met. 我们很久没见面了。
How time flies!It's three months since I saw you last time.时间过得真快!我们有三个月没见面了。
I'm writing to thank you for your help during my stay in America. 我写信是为了感谢你对我在美国期间的帮助。
I am looking forward to receiving your letter. 我期待你的来信。
Thank you in advance. 提前谢谢你。
Please write to me as soon as possible. 请尽快回信。
Good luck./Wish you the best of luck. 祝你好运!
With best wishes. 致以我诚挚的祝福。
Wish you success. 祝你成功。
Wish you a pleasant journey. 祝你旅途愉快。
Please remember me to your family. 请代我向你的家人问好。
I'd appreciate it if you could reply earlier. 请尽快回信，我将不胜感激。
Thank you so much for... 非常感谢……
I would like to thank you from the bottom of my heart for...我由衷地感谢你……
I'm writing to express my sincere gratitude for... 写此信来表达我的诚挚谢意……
I'm grateful to you for... 因你……，我深表谢意。
I truly appreciate your... 我真诚感谢你……
Words fail to convey my gratitude to you. 我对你的感激之情难以用言语表达。
I take the opportunity to express to you my deep appreciation for... 我借此机会向你表达我深深的谢意……
It's kind and generous of you to do this for me and I do appreciate it more than I can say. 你如此善良和慷慨地帮助我，我不胜感激。
I am writing to extend my sincere gratitude for___________(感谢的原因).If it had not been for your assistance in_____________(对方给你的具体帮助)，I fear that I would have been_______(没有对方帮助会产生的后果).
Everyone agrees that it was you who______________(给出细节).
Again，I would like to express my warm thanks to you!Please accept my gratitude.
I would like to express my apology for... 对于……，我想要表达我的歉意。
Will you be good enough to excuse me for.../Excuse me for... 请原谅我……
Please accept my sincerest and deepest apology for... 请接受我最真诚的致歉……
I'm terribly sorry to tell you that.../I regret to inform you that... 很抱歉地告诉你……
I write to you to express my deep regret. 我写此信向你表示深深的懊悔。
I am writing to apologize to you for... 我写信向你致歉，因为……
Would you mind if I...?你是否介意如果我……?
To make up my thoughtless behavior，I... 为了弥补我欠考虑的行为，我……
I wish I could be given a chance to make up for my inconsideration. 我希望你能给我一个机会来弥补我的考虑不周。
I am truly sorry that________(道歉的原因).
The reason is that_________(介绍原因).Once again，I am sorry for any inconvenience I've caused. Hope you can accept my apologies and understand my situation.