If an office asks you to enclose a self-addressed return Letter Pack, write the address where you want the returned documents delivered in the return pack’s お届け先 (recipient) field. The outer envelope travels to the office; the enclosed return pack will travel back to you. They have different destinations.
The instructions below concern document returns within Japan. Follow the receiving office’s current checklist if it specifies Light, Plus, a particular address format, or how to complete the sender field.
Separate the two journeys before you write
Imagine you are sending a certificate request from your home to a university office. This is an illustrative example, not a university’s application form.
| Envelope | Journey | Recipient field | Sender field |
|---|---|---|---|
| Outer mailing envelope | You → university office | The office’s published application address | Your name and address |
| Enclosed return Letter Pack | University office → you | Your return delivery address and name | Follow the office’s instructions; do not automatically copy your own details |
On the return pack, include your postal code, building name and room number where applicable. Use an address at which you can receive the documents when they are actually sent, rather than automatically using the address from an old application.
If the office has not explained the ご依頼主 (sender) field, ask whether it should be left for staff to complete. Do not invent the name of a department or staff member. For the structure of a Japanese address, see our envelope-address guide.
Buy the type the office requests
Japan Post’s current domestic Letter Pack prices and conditions, checked September 28, 2026, are:
| Type | Prepaid price | Thickness and weight | Delivery |
|---|---|---|---|
| Letter Pack Light, blue | ¥430 | Up to 3 cm thick and 4 kg | Mailbox |
| Letter Pack Plus, red | ¥600 | Up to 4 kg; may exceed 3 cm within the service’s envelope conditions | Hand delivery with receipt seal or signature |
Both use Japan Post’s designated envelope and include tracking. Neither is an international return envelope. Check Japan Post’s service conditions for excluded contents and packing requirements; tracking does not mean loss or damage compensation is included.
Do not substitute a different type just because it costs less. For example, the University of Tokyo Faculty of Engineering’s certificate FAQ accepts Letter Pack Light as a return-envelope option. Keio’s alumni certificate page also describes a domestic Letter Pack Light return, while directing applicants to campus-specific instructions. These examples demonstrate an actual use case, not a rule for all institutions.
Enclose the empty return pack without sealing it shut
The office still needs to put your documents into it. Complete the requested address fields and leave the return pack’s sealing strip unused. Put that return pack inside your outer mailing envelope with the other required documents.
Check the office’s directions before folding the return pack or choosing an outer envelope. If documents must remain unfolded, do not infer that any small envelope will work. Our A4 document mailing guide compares folded, flat and tracked outward-mail options.
The prepaid return pack covers its own return journey. You still need postage for the outer envelope. Weigh and measure the outer envelope after adding the empty return pack and your documents; the additional material is part of what you are mailing.
Keep outward and return tracking numbers separate
If the outward journey also uses a tracked service, there will be two different tracking references. Record which belongs to which journey before handing over the outer envelope. Follow the office’s directions about the return pack’s tracking sticker, and take a note or photo of the number without obscuring the label.
An outward delivery confirmation means the office received that mailing. It does not mean the office has finished processing the request or dispatched your return documents. A return tracking number alone also does not establish a posting date. Ask the office about processing time when a deadline matters.
What if the documents need to come back overseas?
Do not write a foreign address on a domestic Letter Pack and expect it to become international mail. Ask the office which overseas return method it supports. Keio’s cited page, for example, distinguishes a domestic Letter Pack Light return from an international EMS arrangement; other offices may have different procedures.
Avoid copying an old fee from an application example. Japan Post’s current rates and the office’s current return instructions need to agree before you send the request.
Before closing the outer envelope
- The outer envelope points to the office; the return pack points to your return destination.
- You used the requested return service and completed only the fields the office asks you to fill.
- The return pack is empty and unsealed, with its address and barcode readable.
- The outward postage includes the weight and dimensions of everything enclosed.
- Any tracking numbers are labelled “outward” and “return” in your own records.
This guide explains envelope preparation. It does not replace an institution’s document checklist, processing rules or deadline instructions.