Second Circuit Holds That the Hague Service Convention Prohibits Email Service on Mainland China-Based Defendants

In Smart Study Co., Ltd v. Shenzhenshixindajixieyouxiangongsi, — F.4th —, No. 24-313 (2d Cir. Dec. 18, 2025), the United States Court of Appeals for the Second Circuit addressed a question of first impression at the federal appellate level: whether the Convention on Service Abroad of Judicial and Extrajudicial Documents in Civil and Commercial Matters (the “Hague Service Convention”) permits email service of process on mainland China-based defendants. The court held that it does not. As a result, the court held that Rule 4(f) of the Federal Rules of Civil Procedure bars email service on mainland China-based defendants with known physical addresses.

Facts and Procedural History

Plaintiff Smart Study is a South Korean entertainment company that owns the trademarks for the popular “Baby Shark” song. It sued dozens of mainland China-based defendants for allegedly manufacturing and selling counterfeit Baby Shark products. To stop the alleged counterfeiting, Smart Study brought suit in the Southern District of New York. Smart Study filed an ex parte motion seeking temporary restraining orders, an order to show cause as to why preliminary injunctions should not be issued, and permission to serve the defendants by email pursuant to Rule 4(f)(3) of the Federal Rules of Civil Procedure, which states that a party may be served outside the US “by other means not prohibited by international agreement, as the court orders.” The district court granted Smart Study’s motion, and Smart Study subsequently served all defendants by email. When no defendant responded to the district court’s show cause order, the district court entered a preliminary injunction barring all defendants from manufacturing or selling counterfeit Baby Shark products.

Several months later, two defendants appeared and moved to dissolve the injunction on the ground that the district court lacked personal jurisdiction because the email service on them violated the Hague Service Convention. Before the court ruled on this issue, Smart Study voluntarily dismissed the two defendants from the action. It then moved for default judgment against the remaining defendants. The district court denied the motion. It concluded that the Hague Service Convention bars email service on mainland China-based defendants and it therefore lacked personal jurisdiction over the remaining defendants.

Smart Study then filed a renewed motion for partial default judgment, asserting that the Hague Service Convention did not apply to 49 of the defendants because their physical addresses could not be obtained despite reasonable diligence. The district court agreed and granted the motion. The district court then ordered Smart Study to show cause as to why the actions should not be dismissed as to the two remaining defendants – Shenzhenshixindajixieyouxiangongsi and Changgesshangmaoyouxiangongsi – whose addresses in mainland China were known to Smart Study, for failure to serve in accordance with Rule 4(f). Smart Study again argued that the Hague Service Convention does not prohibit email service and therefore, its email service of the two defendants was proper under Rule 4(f)(3). The district court disagreed. Smart Study appealed.

The Second Circuit’s Reasoning

Service under Rule 4(f)(3). The court began its analysis with Rule 4(f)(3). Because Smart Study had the district court’s permission to serve the two defendants by email, the key question for the Second Circuit to address was whether the Hague Service Convention permits email service on mainland China-based defendants. The court held that it does not:

• Mainland China’s Article 10 objection is dispositive. Article 10(a) of the Hague Service Convention reads: “Provided the State of destination does not object, the present Convention shall not interfere with the freedom to send judicial documents, by postal channels, directly to persons abroad.” Because Article 10(a) is prefaced with the phrase “provided the State of destination does not object,” and because mainland China has objected to service methods under Article 10, the Second Circuit held that email service cannot be proper if “postal channels” were interpreted to include email.
• The Convention is exclusive where it applies. Relying on the Supreme Court’s decision in Water Splash, Inc. v. Menon, 581 U.S. 271 (2017), and the text and structure of the Hague Service Convention, the Second Circuit further held that the Hague Service Convention creates a closed universe of permissible service methods and “pre-empts inconsistent methods of service wherever it applies.” Accordingly, even if “postal channels” were interpreted to exclude email, service by email would still be impermissible because email is not a permissible service method specified in the Hague Service Convention. Although the court acknowledged that email service offers advantages in speed and cost, it concluded that such considerations cannot override the Convention’s mandatory framework.

Because the court held that email service would be impermissible under either interpretation of Article 10(a), it left open the question of whether the phrase “postal channels” encompasses email.

To avoid the problems raised by the Hague Service Convention, Smart Study attempted to read an emergency exception into Rule 4(f)(3), arguing that the rule functions as an “alternative to compliance with the Hague [Service Convention]” in “exigent circumstances.” The court summarily rejected Smart Study’s position, finding no textual support in the rule for an “emergency exception”.

Service under Rule 4(f)(2). Smart Study argued in the alternative that service was proper under Rule 4(f)(2) of the Federal Rules of Civil Procedure, which permits service “as prescribed by the foreign country’s law for service in that country in an action in its courts of general jurisdiction.” The court rejected this contention because Rule 4(f)(2) applies only “if there is no internationally agreed means, or if an international agreement allows but does not specify other means.” The court held that this condition was not satisfied because the Hague Service Convention applied and prohibits email service in mainland China.

Takeaways

While the court acknowledged the “difficulties companies face in policing trademark- and copyright-infringement abroad, particularly in China,” its conclusion was unequivocal: where the Hague Service Convention applies, email service on mainland China-based defendants is impermissible.

This decision has several practical implications for litigants:

1. Plaintiffs should plan for service early. For plaintiffs suing mainland China-based defendants, service strategy must be front-loaded. Plaintiffs should assess service options using the following framework:
1. Can the defendant be served within the United States? Plaintiffs should first assess whether the defendant can be served validly within the United States in a manner that does not engage the Hague Service Convention. Among other possibilities, plaintiffs should consider whether the defendant has any US-based officer, managing or general agent, or any other agent authorized by appointment or by law to receive service of process such that the defendant can be served in accordance with Rule 4(h)(1)(b) of the Federal Rules of Civil Procedure.
2. If the defendant cannot be served within the United States:
1. Is the defendant’s foreign address known? If so, then plaintiffs should assume that Convention-compliant service will be required and should structure case timelines accordingly, particularly in actions seeking preliminary injunctive relief or default judgment.
2. Is the defendant’s foreign address unknown? If so, then the Convention does not apply. Alternative service under Rules 4(f)(2) and (3) may be available, provided it satisfies due process. Because this distinction is now dispositive, plaintiffs should carefully document their diligence efforts, including, for example, internal investigations, platform or vendor data, third-party investigators, and sworn declarations establishing that the address could not reasonably be obtained.
2. Defendants should closely evaluate whether service was proper. This decision underscores that improper service defeats personal jurisdiction and can undermine default judgments or preliminary injunctions, which will be more difficult to obtain and defend unless service issues are resolved properly. Mainland China-based defendants, especially those served via email, should carefully evaluate:
1. Whether the plaintiff knew or should have known the defendant’s physical address;
2. Whether the service complied with the Hague Service Convention and the Federal Rules of Civil Procedure; and
3. Whether any defaults, injunctions, or asset restraints were entered without proper service.
3. Hong Kong-based defendants may warrant different treatment. Parties should note that the outcome may differ for defendants based in Hong Kong rather than mainland China. Unlike mainland China, Hong Kong has not objected to Article 10 of the Hague Service Convention. As a result, for Hong Kong-based defendants, the permissibility of email service may turn on the question the Second Circuit left open in Smart Study, namely whether “postal channels” within Article 10 of the Hague Service Convention encompass email. Practitioners litigating against or on behalf of Hong Kong-based defendants should monitor developments on this issue and consider alternative methods of service in the interim. (See, e.g., Kangol LLC v. Hangzhou Chuanyue Silk Import & Export Co, currently pending before the Seventh Circuit –although because the defendant-appellant also is based in mainland-China, the court may leave the interpretation question open as the Second Circuit did.) 

As further explained in the Terms / Notices linked below, the information provided herein is not legal advice. Any information concerning the People’s Republic of China (PRC) is not an opinion on, determination on, or certification of the application of PRC law. We are not licensed to practice PRC law.