Short answer. The person to whom a letter is addressed and delivered owns it, but owning it does not mean he may publish it. Article 723 says private letters cannot be published or disseminated without the consent of the writer or his heirs. So the recipient keeps the paper, while the writer keeps control over publication.
What the law says
cannot be published or disseminated without the consent of the writer or his heirs
Civil Code, Article 723 — Ownership Of Private Letters. Read the full provision →
The recipient owns the letter itself
Article 723 begins by settling ownership: letters and other private communications in writing are owned by the person to whom they are addressed and delivered. Once a letter has been sent and received, the physical document belongs to the recipient. He can keep it, store it, or destroy his own copy; the paper is his property. This covers not just letters in the old sense but private communications in writing generally. What the law separates, though, is ownership of the object from the right to make its contents public. Holding the letter in your hands is one thing; broadcasting what it says is another, and the two do not travel together.
Owning it does not mean you can publish it
This is the part that surprises people. Even as owner, the recipient cannot publish or circulate the letter without the consent of the writer or his heirs. Publication and dissemination cover more than printing in a book; sharing the contents widely, posting them online, or handing out copies can all fall within the ban. The right to decide whether private words go public stays with the person who wrote them, and after that person dies, it passes to the heirs. So a recipient who releases the letter's contents to the public without that consent acts beyond what his ownership allows and may expose himself to liability.
When a court may allow publication
The consent rule is not absolute. Article 723 adds that the court may authorize their publication or dissemination if the public good or the interest of justice so requires. This gives the courts a narrow power to override the writer's refusal when a larger interest is at stake, for example when the letter is needed as evidence or when disclosure serves a genuine public concern. It is the court, not the recipient, that makes this call, and only in the situations the article names. A private individual cannot decide for himself that the public good justifies publishing; he must let a court weigh it.
What this protects, and its limits
The provision protects privacy and the confidential character of personal correspondence, whatever its monetary value. It matters today for messages that feel modern but are still private writings. Note what the rule does and does not do. It governs publication and dissemination, not private reading; the recipient is free to read what was sent to him. It also does not, by itself, resolve related questions such as defamation or breach of confidence, which other laws address. Whether a particular sharing counts as publication, and whether consent or a court order is needed, depends on the specific facts, so this is general information rather than advice.