国际预付费信封(Prepaid Envelope)
https://www.fedex.com.cn/en-us/shipping/create-shipping-label.html
https://shipsigma.com/blog/how-do-fedex-prepaid-labels-work
回邮信封的准备方法：（请详细填写寄件人和收件人信息）
人在澳洲：
选择澳洲邮局提供的澳洲快递C5预付费信封、国际快递C5预付费信封或国际普通预付费信封（请勿使用挂号信封，无法追踪查询）
人在国内：
回邮信封只能使用澳洲预付费信封或粘贴澳洲邮票；没有澳洲信封时，请联系澳洲朋友购买；
四、文件邮寄
邮寄办理时可以同时邮寄多人材料，共用一个B4回邮信封。
将上述文件装入回邮信封，填写邮寄地址；
国际预付费信封(Prepaid Envelope)
主要有2种形式（note：有可能找该国当地的小的delivery或shipping公司购买，也可以论坛上找人）
（1）一种是购买邮局（Post Office）的邮票，信封无所谓自己做还是买的。一般这种邮票不好买，当地的人当地邮局买邮票好买。或者让该国的人邮局买一些带回来储备。
（2）另一种是邮局公司预付费信封，看看各大邮局公司官网购买。比如
英国：
https://shop.royalmail.com/postage-and-packaging/envelopes/prepaid 。不知道是否可以国际
美国：
https://www.postaltimes.com/postalnews/usps-to-end-prepaid-flat-rate-stamped-envelopes/ （可惜美国的这个预付费要停售了）
https://www.ups.com/us/en/help-center/sri/ctc15.page (仅限美国）
西班牙：
https://www.correos.es/es/en/individuals/send/envelope-and-packaging/prepaid
新西兰：
澳洲：
https://www.gatesplus.com.au/pdf/OverseasParcels.pdf
https://auspost.com.au/sending/send-overseas/registered-post-international
爱尔兰：
https://www.anpost.com/Shop/Stamps-labels/National-Stamps 境内
加拿大：
匈牙利：
https://www.posta.hu/sending_mail/letters_abroad/international_prepaid_envelope
法国：
The common solution to the general problem of how to send mail to a recipient in a foreign country and pay for them to send it back to you is the International Reply Coupon, which is overseen by the Universal Postal Union (of which France and the United States are both members). From Wikipedia:
An international reply coupon (IRC) is a coupon that can be exchanged for one or more postage stamps representing the minimum postage for an unregistered priority airmail letter of up to twenty grams sent to another Universal Postal Union (UPU) member country. IRCs are accepted by all UPU member countries.
UPU member postal services are obliged to exchange an IRC for postage, but are not obliged to sell them.
The purpose of the IRC is to allow a person to send someone in another country a letter, along with the cost of postage for a reply. If the addressee is within the same country, there is no need for an IRC because a self-addressed stamped envelope (SASE) or return postcard will suffice; but if the addressee is in another country an IRC removes the necessity of acquiring foreign postage or sending appropriate currency.
In France, IRCs can be purchased online from La Poste for 1,30 euros plus shipping (search for "coupon-réponse international"). You can also try to ask at a post office, but in my experience it is likely that they won't even know what it is.
In this case, looking at the provided link it is unclear whether the recipient will accept an IRC as postage; in general one should always confirm this with the recipient beforehand since the recipient still has to exchange the IRC for actual stamps.
意大利
Note：还有一种方式就是直接多付费。（意大利）
The comunes always require a written request. When I requested a birth certificate from my comune, along with the letter I sent a self addressed envelope and 5 euros for 'postage' or whatever they wanted to use it for. A month or so later I received the certificate and to my surprise they gave me the 5 euros back. So maybe you could attempt the same and add an additional note saying there's no way for you to obtain italian postage, but here are some euro's to pay for it.
In case anybody runs into this question again, I am posting what I ended up doing. Following Rossonero's advice, I sent a written request to my comune requesting a copy of the birth certificate along with a letter, a return envelope with my address, copy of my photo identification, and 15 euros. I dropped my request into the mail on March 15th and received a copy of the birth certificate yesterday (April 2nd)--a faster turnaround time than my request for documents from the USCIS, which was made the same day. 15 euros was more than enough to cover return postage as the Italian post mark indicated the cost for return postage was 4.5 euros from Bari to my home in Fort Collins, CO. I hate sending cash in the mail, but it ended up working out this time.
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0.A self-addressed envelope enclosed with the postage fee (equivalent to sevenInternational Postage Vouchers which can be purchased at your local post office)11.There are special submission requirements(more detail see Document Preparation)--泰国无犯罪
https://international.thailandpost.com/services/registered/?lang=en 泰国估计只有邮票，没有预付费信封。
o send your documents to you by post, you will need to provide us with an address, other than a P.O. Box. You must provide a PRIORITY COURIER prepaid envelope or, preferably, XPRESS POST from Canada Post.
In any case, the Consulate General will not be responsible for problems, delays or loss of documents sent by mail.
The form can be collected from the Consular Section, or you can request for the form to be posted to you, by supplying us with an A4 stamped addressed envelope, with a 1st class LARGE stamp.
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pre-paid envelope
A self-addressed, pre-paid envelope from DHL, United States Postal Service or FEDEX only with tracking. Receipt of payment for the envelope must be attached. Please do not send UPS envelopes.;
https://egyptianconsulate.ca/police.html 这个视频有1分20秒有预付费的信封
The letter and attachments must be sent by DHL, having paid all shipment and return charges
For sending the police certificate back to the applicant outside Zimbabwe the applicant must send together with a fingerprint card a pre- paid self-addressed envelope by either DHL or FEDEX. The fee for a police certificate must be paid to the following bank.
Applicants should make arrangements with the post/DHL/FEDEX for pre-paid return postage.
A pre-paid DHL envelope for them to return the police certificate to you
https://www.xiaohongshu.com/discovery/item/60afcbea0000000021034afc
https://www.smartcapitalmind.com/what-is-a-prepaid-envelope.htm