As you can see from the photo above, certain countries are subject only to EMS and Air Mail, where others have had a total suspension of service for all types of mail.

As per the Japan Post website:

"The novel coronavirus pandemic has caused many countries/territories to take measures such as stopping acceptance of inbound postal items as well as considerable suspension and reduction of flights from/to Japan. Accordingly, our transportation performance has significantly declined. Therefore, acceptance of international mail items, mainly EMS and parcel-post/letter-post items by air and SAL, will be temporarily suspended from April 2. For details, please see the attachment (PDF16KB).

Items which have already been accepted and cannot be dispatched to their destinations will be returned from the delivery offices to the senders in order. In addition, because of the global reduction of flights, considerable delivery delays are expected for outbound mail items to other countries/territories."

The list is subject to change as circumstances change around the globe, so be sure to check the Japan Post website for updates as they become available. You can see the full list of restrictions in Japanese here.

Update
Due to the decrease in air traffic, postal services to and from the United States will also temporarily be suspended. We will keep you posted on any further changes.