Key takeaways

  • On September 25, 2026, Japan Post found possible unauthorized access to the server behind its online inquiry service for international mail (調査請求Web受付サービス).
  • The service is a pilot running only at post offices in Kanagawa and Yamanashi prefectures. It has been suspended, with no restart date.
  • Japan Post says the cause and scope are under investigation. It has not said whether any personal data was accessed.
  • The same-day notice mainly explains why the service is offline. The harder question, whether customer data was exposed, is still open.

What happened#

Japan Post published a short notice on September 25. According to the notice:

  • At around 15:00 JST that day, Japan Post found that the server used by its international mail inquiry web service may have been accessed from outside without authorization.
  • The cause and the extent of the impact are under investigation.
  • The service has been temporarily suspended. Japan Post will announce a restart on its website.

The notice's title refers to "unauthorized access, etc." (不正アクセス等), which leaves open whether other kinds of incidents are involved. It gives no further detail.

What the service does#

The inquiry service lets customers ask Japan Post to trace international mail that has not arrived, arrived damaged, is missing contents, or is delayed. Customers can file the request online instead of filling in a paper form at a post office counter.

According to trade press reports:

  • The service started as a pilot in February 2026, limited to post offices in Kanagawa and Yamanashi prefectures, excluding small contracted branches.
  • It covers EMS, registered mail, small packets, printed matter, international air parcels and international parcels.
  • Customers link shipping records from Japan Post's International Mail My Page service and enter the item's tracking number to file a request.

Paper inquiries at post office counters are still available while the web service is down.

What we don't know yet#

Japan Post has not said:

  • Whether any data on the server was viewed or taken
  • What data the server held, or how many customers used the service
  • How the possible access was detected, or how the attacker got in
  • Whether the linked My Page service is affected

Because the service works with shipping records for international mail, the data involved could include details of both senders in Japan and recipients overseas. That is a possibility, not something Japan Post has confirmed.

Our analysis: the notice explains the outage, not the exposure#

Japan Post announced the problem on the same day it found it. That speed is natural here. The service had to be taken offline, and customers who try to use it need to know why. In Japan, notices about a service being stopped tend to come out quickly. Notices about data being exposed usually take much longer, because organizations wait until they can say whose data was affected.

We saw that pattern in the Digital Agency breach. The agency went public eleven weeks after detection, once it had identified the people affected.

So the real test for Japan Post is the follow-up. The questions that matter are:

  • Did anyone actually get into the server?
  • What customer data did it hold?
  • Were the linked shipping records exposed?
  • What should customers watch for?

"Under investigation" is a reasonable first answer. The question is how long it remains the only one. We will be watching for that follow-up.

What this means for readers#

  • If you used the service, or sent international mail from Kanagawa or Yamanashi and filed an online inquiry, watch for a follow-up notice from Japan Post. Be wary of unexpected messages about your parcels. Japan Post's name is already one of the most common lures in phishing texts in Japan.
  • If you received international mail from Japan, there is no indication yet that recipients' details were involved. We will update this article if that changes.

Japanese terms at a glance#

Japanese Reading Meaning
調査請求 chōsa seikyū Inquiry (trace) request for lost, damaged or delayed mail
不正アクセス等 fusei akusesu tō "Unauthorized access, etc."
原因および影響範囲については、現在調査中 gen'in oyobi eikyō han'i ni tsuite wa, genzai chōsa-chū "The cause and scope of impact are under investigation"
一時的に受付を停止 ichijiteki ni uketsuke o teishi Temporarily suspended

We will update this article when Japan Post publishes more.