No. Japan Post’s counter-based content-certification service, 内容証明 (naiyo shomei), accepts one content document and does not allow other items, including a reply envelope or drawing, to be enclosed with it. Do not prepare it as an ordinary letter packet containing a letter plus supporting materials. Japan Post: eligible documents
Decide whether you need certification of the document
Content certification records what document was sent, when, and from whom to whom, using the copies prepared by the sender. Japan Post does not certify that the statements in the document are true. Japan Post: content-certification overview
That distinction matters before you choose a mailing method. If your practical task is simply to get a set of materials to someone, putting “content certified” on the plan does not make all those materials eligible. If certification is specifically required, build the mailing around the eligible document and treat other materials as a separate question.
This guide concerns postal preparation. It does not tell you whether content certification is legally necessary, what a notice should say, or whether sending it separately from other materials would meet a contractual deadline.
Sort the packet into three groups
Consider a hypothetical packet containing a letter, two copies of that letter, a reply envelope and a drawing. It is an invented planning example.
| Item on your desk | What to do before the counter visit |
|---|---|
| Document intended for the recipient | Check that it meets the content-document conditions |
| Two copies for retention | Prepare them for the sender and post office, rather than treating them as extra recipient enclosures |
| Reply envelope and drawing | Keep them out of the proposed content-certified envelope |
The counter procedure asks for the content document, two copies, an envelope bearing the sender’s and recipient’s names and addresses, and the required postage and charges. The copies are retained separately by the sender and post office. Japan Post: items to submit
Removing the prohibited extras does not by itself certify that the remaining document is compliant. Check the writing and copy-format conditions next. If the other materials still need to be sent, confirm the recipient’s instructions and the purpose of the mailing before arranging another suitable service; this article does not promise that two separate mailings are interchangeable with one certified packet.
“One document” does not mean “one sheet”
Japan Post’s conditions expressly address retained copies running to two or more sheets, including requirements for seals across their joins. Do not shorten or omit necessary text merely because you read “one document” as “one page.” The same conditions distinguish character and line limits for the retained copies from the content document itself. Japan Post: copy preparation and multi-sheet rules
An English-language guide also does not mean that any English letter is accepted. Japan Post lists permitted characters and restricts Roman letters to proper nouns for this service. Check the actual document against that rule instead of assuming that an English translation can be submitted unchanged. The service also requires general registered mail, 一般書留. Japan Post: characters and registration conditions
Confirm the handling office before making the trip
Not every post office handles content certification. Japan Post identifies delivery post offices and other designated offices, and notes that some handling offices offer it only on specified days. Use the official handling-office information before travelling. Japan Post: where to submit
Before you leave, be able to point to the recipient’s document, the two retained copies and the addressed envelope as separate items. Ask the office to resolve any uncertainty about format before treating the packet as ready to send. The useful final check is not “Have I put everything in?” but “Have I prepared only the permitted document, with the required copies separately available?”
This article is desk research checked on 29 October 2026, not an actual counter visit. It covers the physical counter service; the electronic service has its own preparation process. It does not assess the legal effect of a particular document or guarantee acceptance of a document we have not examined.