英文回函的格式通常包括以下幾個部分：
開場語：如"Dear Sir or Madam"，表示對收件人的尊重。
感謝：對收件人的來函表示感謝，如"Thank you for your inquiry dated 25 March"。
回復內容：針對收件人的請求或問題進行回復，可以是一致的同意或拒絕。
理由：提供拒絕或不能同意請求的具體原因，如"The fact is that most of our competitors also keep such information private and confidential"。
希望：表達希望對收件人有所幫助的願望，如"If there is any other way in which we can help you, do not hesitate to contact us again"。
結尾：使用禮貌的結束語，如"Truly yours"，並附上簽名。
以下是一份英文回函的範文：
```
Dear Sir or Madam,
Thank you for your inquiry dated 25 March. We are always pleased to hear from a valued company. I regret to say that we cannot agree to your request for technical information regarding our products. The fact is that most of our competitors also keep such information private and confidential. I sincerely hope that this does not inconvenience you in any way.
If there is any other way in which we can help you, do not hesitate to contact us again.
Truly yours,
[Your Name]
[Your Title]
[Your Company]
[Your Contact Information]
```
請根據實際情況調整上述內容，以確保回函的準確性和適當性。