Here are a few options for a description for the WordPress post_tag “存證信函” in Traditional Chinese, offering slightly different nuances:

**Option 1: Simple & Direct**

* **Description:** 法律文件，用於記錄郵寄內容並證明已送達。

* **(Translation):** Legal document, used to record the content of a mailing and prove delivery.
* **(Why it’s good):** Concise, clear, and accurate. Gets straight to the point about the function of this letter type.

**Option 2: Explanatory & Informative**

* **Description:** 一種具有法律效力的郵件，寄件人透過郵局證明已向收件人發出信函，並保留郵寄內容的副本。 常用於法律爭議的起始。

* **(Translation):** A legally binding mail, through which the sender, via the post office, proves that they have sent a letter to the recipient and retains a copy of the mailing content. Often used at the beginning of legal disputes.
* **(Why it’s good):** Provides a bit more context, explaining the legal nature and common use of the letter.

**Option 3: Focusing on the Practical Use**

* **Description:** 寄出正式通知或請求的法律文件，可用於通知、催繳、警告等，保留證據以保障權益。

* **(Translation):** A legal document for sending formal notifications or requests, used for notifications, dunning, warnings, etc., preserving evidence to protect one’s rights.
* **(Why it’s good):** Highlights the practical uses of the letter, the things it can be used for, and the benefits for the person sending it.

**Option 4: Concise and Keyword Focused (Good for SEO)**

* **Description:** 存證信函，法律，通知，證據，郵寄。

* **(Translation):** Certified Letter, Law, Notice, Evidence, Mailing.
* **(Why it’s good):** Uses important keywords, making it easier for people to find content related to this topic with search. It is very short.

**Recommendation:**

Choose the option that best fits the overall tone and purpose of your blog or website.

* If your blog is about law/legal advice, then **Option 2 or 3** would be more appropriate.
* If you just need a brief description for the tags, **Option 1 or 4** would be fine.
* **Option 4** is likely better if you are optimizing for search engines, though its description is minimal.

Remember to place the chosen description into the “Description” box when creating or editing the “存證信函” tag in your WordPress tag settings. Good luck!