Without delay = quickly
To get back to someone = To reply or respond to someone's query or question.
A swift reply = A quick reply.
A rapid response = A quick reply.
Instead of saying 'Thanks,' a slightly more formal way would be to say:
"I appreciate...." or, "I really appreciate..."
Without delay = すばやく
To get back to someone = 人の質問に[返信](https://eikaiwa.dmm.com/uknow/questions/35189/)、返答すること
A swift reply = 素早い返信
A rapid response =素早い返信
'Thanks,'という代わりに、もう少しフォーマルに言うのであれば、
"I appreciate...."（....して頂き[感謝します](https://eikaiwa.dmm.com/uknow/questions/42579/)） 又は"I really appreciate..."（....して頂き本当に感謝します） です。
"Thank you for quickly replying to my message."
quickly - fast
Replying - answer
Message - this could be a text message, email, voice message, etc.
"I appreciate your swift response to my email."
Appreciate - this is something you are grateful or thankful for. The person chose to answer you quickly and you appreciate them doing that for you.
Swift - quick or fast
Response - Answer, sending their own email
"Thank you for quickly replying to my message."
わたしのメッセージに早速返信してくれてありがとう。
quickly - はやく
Replying - 返信する
Message - テキスト、Eメール、留守電など
"I appreciate your swift response to my email."
私のEメールに早く返信してくれてありがとう。
Appreciate - 感謝すること。返信を早くしてくれた人に感謝しているという意味です。
Swift - はやい
Response - 返信する
The two sentences you see provided above are great ways to express to your listener that you are grateful that they responded to your email quickly. In the first sentence you will see the adjective swift and in the second sentence you will see the adverb promptly. Both of these words mean quick or quickly. They would make excellent additions to your vocabulary.
"Thank you for getting back to me so quickly." is the most common. "getting back to" is a respectful and formal way of saying "reply".
"Thanks for responding in a timely manner." is more formal than the first phrase. "a timely manner" means a time period that is appropriate to respond to an email.
"I appreciate your fast response." instead of saying "thank you" you can be more direct about how it makes you feel by saying "I appreciate".
"Thank you for getting back to me so quickly."（早急な返信ありがとうございます）
- これが最も一般的です。"getting back to" は "reply"（返事する）の丁寧でフォーマルな言い方です。
"Thanks for responding in a timely manner."（早急な返信ありがとうございます）
- これは最初のフレーズよりもフォーマルです。"a timely manner" はメールを返信する適切なタイミングを表します。
"I appreciate your fast response."（早急な返信に感謝致します）
- "I appreciate" は "thank you" よりも自分の気持ちを直接的に表します。
Business email messages can range from very formal to casual depending on your business partner and how familiar the relationship is. If you would like to be very proper and formal, you could use the phrase- "Thank you for your prompt reply." If you have a casual relationship, then you can instead use the word, "Thanks." To use the phrase, "quick reply" is also grammatically correct but it sounds less formal than using the phrase, "prompt response."
ビジネスメールは相手や相手との関係によってカジュアルなものもあればとてもフォーマルなものもあります。
とても丁寧、フォーマルに言いたいなら、
"Thank you for your prompt reply."（素早いお返事ありがとうございます）
というフレーズが使えます。
相手と親しいなら、代わりに "Thanks" という単語が使えます。
"quick reply"（素早い返事）を使っても文法的に正しいです。ただ、これは "prompt response" よりもインフォーマルです。
You can use any one of these two statements to thank someone for a prompt reply:-
1. Thank you for your prompt reply.
2. Thank you for your timely response.
If you thank someone for a prompt or timely response to your email, it means that that the person responded withour delay to your email. The words "timely" and "prompt" indicate that the response was without delay.
次の二つの文で素早い返信に感謝できます。
1. Thank you for your prompt reply.（素早いお返事ありがとうございます）
2. Thank you for your timely response.（素早いお返事ありがとうございます）
"prompt reply" または "timely response" は、相手がメールに対して速やかに返事をくれたことを表します。"timely" と "prompt" は、返信に遅れがなかったことを表します。
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