Postage for Letter to Canada
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March 14, 2024
Imagine you’re sitting somewhere in New York, United States, writing a heartfelt letter to a friend in Toronto, Canada.
You fold the stationery neatly, put it in an envelope, and decide to send the letter through USPS (United States Postal Service).
But wait, how do you mail a letter to Canada? How much does USPS charge for letters addressed to Canada? What are the specific requirements for this shipment?
FindPostOffice.org is your go-to online resource for vital information regarding post offices in the U.S.
This article explains the process of sending mail and packages to Canada, including letters.
Whether you want to send warm regards or time-sensitive business correspondence or are just curious about the “how-tos” of mailing to Canada, this article can help you.
Read on to understand various USPS postage options for sending items to Canada.
Sending Mail to Canada: What You Need To Know
Sending mail to Canada isn’t that complicated once you understand the process. The following sections discuss what sending mail to Canada involves, including its cost.
Package Postage to Canada
First Class Package International Service (FCPIS) is USPS’ lowest-cost option for shipping packages weighing up to four pounds.
You can access this service for only $14.11, which makes it ideal for mailing products under $50. FCPIS also offers free tracking information for items sent to Canada.
FCPIS shipments generally take 11 to 20 business days.
Postcard Postage to Canada
With USPS, sending a postcard or letter from the U.S. to another country, including Canada, is easy and affordable.
For example, you can send a one-ounce letter or postcard using one USPS Global Forever stamp.
The Global Forever stamp allows you to send items to any foreign country where First-Class Mail International service is available.
Letter Mail to Canada
Canada Post, a primary postal operator in Canada, considers the following items as letter mail (first-class mail):
- Personal messages
- Billing statements
- Business correspondence
- Invoices
Picking the Right Mail Carrier
Determining the suitable mail carrier for sending your packages and envelopes to Canada is essential. Various factors determine which courier suits your needs.
For example, the U.S. Postal Service may be the most affordable carrier in the U.S. for shipping to international locations. So, if you want to save money, this might be your ideal delivery service provider.
Mailing Options
USPS offers mailing options for postcards, letters, gift boxes, and large envelopes. The delivery timeframe, postage rates, and tracking services vary depending on the mailing option.
Below are six USPS shipping methods with their features and pricing:
First-Class Mail International
FCMI, or First-Class Mail International, is a cost-effective way to send letters and large envelopes to over 180 countries, including Canada, Australia, and Great Britain.
FCMI is the most affordable international service offered by USPS. Here are additional features of this shipping option:
- Suitable for letters weighing up to 3.5 ounces (oz), postcards, and large envelopes (flats) weighing up to 15.994oz
- Global Forever stamp available
- Delivery time or speed varies by destination
- Can be combined with Registered Mail service in select countries
- Costs depend on weight and destination
First-Class Package International
You can use this service to do the following:
- Get delivery confirmation to specific countries.
- Send parcels weighing up to 64oz or 4 pounds (lbs), worth up to $400, worldwide.
- Retail costs start at $15.75.
Global Express Guaranteed
GXG (Global Express Guaranteed) is the fastest USPS international shipping option with international delivery and transport by FedEx Express.
GXG offers date-certain shipment in one to three business days to over 180 countries with a money-back guarantee.
The cost of shipping a mailpiece via GXG service varies depending on the package’s weight and destination country.
Priority Mail Express International
This service is a reliable, high-speed option for printed matter, correspondence, and parcels. Priority Mail Express International is available to over 180 countries and has the following features:
- Average delivery of three to five business days
Note: The average number of days depends on the mail’s origin and destination.
- Using the USPS Tracking page and typing in the item’s tracking number
As of 2023, Priority Mail Express International costs start at $54.75 (at the post office) and $51.98 (Commercial Base and Commercial Plus).
Priority Mail International
Priority Mail International service is a secure and affordable way to ship to over 180 countries, including Canada, Australia, and Mexico.
You can access this service in two ways:
- Flat-rate option: Ship items using free flat-rate envelopes and boxes.
Note: Small boxes and envelopes weigh up to 4lbs. Medium and large boxes weigh up to 20 lbs.
Prices start at $30.35.
- Ship by weight: For items weighing up to 70 lbs, prices depend on the destination country’s price group. Postage costs start at $42.10.
Priority Mail International for Flat Rate Boxes and Envelopes
As mentioned, USPS offers flat-rate boxes and envelopes with fixed shipping costs between $28.13 and $70.13 to Canada. Meanwhile, postage rates start at $35.01 for all other deliverable countries.
With flat fees, you don’t need to worry about extra charges due to an item’s weight or delivery distance.
How to Calculate Postage From the U.S. to Canada
Postage calculation from the U.S. to Canada is straightforward.
The amount of postage you will pay for package shipments depends on your parcel’s weight, the desired delivery speed, and the package’s origin and destination.
The size and shape of your package may also affect the fee you will pay.
Select Method of Shipment
USPS has a shipping calculator that can help you determine estimated shipment costs.
You will provide the tool with the following information:
- ZIP codes
- Mailing date
- The contents of the shipment
After providing the information above, you will select a USPS shipping method.
The calculator lets you choose from Flat Rate options or shapes like a large envelope, postcard, package, letter, or large package.
Say you choose a flat-rate option, such as the Priority Mail medium Flat Rate box. You can view the expected delivery date and the online and retail postage prices.
However, if you choose a letter, the system will ask you to provide your letter’s weight.
Weigh Your Package
The local post office’s scale is the final judge of your parcel’s weight. However, if you own an accurate scale at home, you can use it to estimate your package’s weight.
Note: The post office weighs items by the ounce.
Calculate Your Postage
As mentioned, the USPS shipping calculator is a tool that lets you enter different inputs such as ZIP codes, destination, mailing dates, service level, and weight to compare rates and delivery times.
You can use the USPS shipping calculator to eliminate any guesswork around shipping rates, allowing you to find the best shipping option for your needs.
Add-On Special Services
You can buy additional services like Certified Mail, additional insurance, or Registered Mail.
Certified Mail gives you a receipt to confirm delivery or delivery attempt.
Registered Mail provides extra protection for valuable customers and internal mail. This add-on offers proof of delivery and mailing.
Purchase and Apply Postage
You can visit the USPS Click-N-Ship (CNS) page to purchase shipping supplies and get postage.
CNS is a program for small businesses and residential customers to order and print online postage.
Meanwhile, you can use alternative postage services, like Stamps.com, to print postage for these shipping services:
- First-Class Package Service
- Parcel Select Ground
- Media Mail
Features and Pricing: Canada Postage Rates
The following sections can help you understand the essential aspects of mailing within the country, from cost considerations to the services offered.
Sending a Letter to Canada: How Much Does It Cost To Mail a Letter to Canada?
First-Class Mail International is an ideal mailing option for sending an envelope of documents weighing under one pound (15.994oz). For this service, letter postage costs start at $3.
Sending a Postcard to Canada: Postage to Canada Prices
A Global Forever stamp is the most convenient way to send a postcard to Canada. As of 2023, the cost of this stamp is $1.50.
Postage Stamps To Mail to Canada
USPS offers Global Forever stamps for international mail. This option might be ideal for you if you intend to send a letter to Canada.
Suppose you want to use domestic stamps. In that case, you should use enough number of these stamps to cover the required value.
Accuracy Notes: Looking Into USPS Rates to Canada
When sending mail or packages to Canada, familiarity with USPS rates is crucial to ensuring accuracy and minimizing costs.
Here’s additional information regarding current costs and price changes at USPS.
New Prices
As of 2023, the postal rates for shipping to Canada are as follows:
- First Class Package International
- Start at $22.23 (commercial)
- Start at $23.40 (retail)
- Priority Mail International
- Start at $39.53 (commercial)
- Start at $42.10 (retail)
- Priority Mail International Flat Rate Envelopes
- $28.57 (commercial)
- $30.35 (retail)
- Priority Mail Express International Flat Rate Envelopes
- $51.98 (commercial)
- $54.75 (retail)
Previous Price Increases
Here’s how much the price of a First-Class stamp has increased since 2012:
- January 2012: 45 cents (¢)
- January 2013: 46 ¢
- January 2014: 49 ¢
- April 2016: 47 ¢
- January 2017: 49 ¢
- January 2018: 50 ¢
- January 2019: 55 ¢
- August 2021: 58 ¢
- July 2022: 60 ¢
- January 2023: 63 ¢
- July 2023: 66 ¢
Holiday Shipping Rate Increase Info
The USPS can impose a temporary shipping rate increase during the holiday season.
For example, USPS temporarily increased the postage rate from October 2, 2022, to January 22, 2023.
The rate hike affected First Class Package Service, Priority Mail Express, Priority Mail, USPS Retail Ground, and Parcel Select.
First Class Mail International Postage to Canada
As shown above, shipping a one-ounce postcard or letter internationally using a First-Class Mail’s Global Forever stamp costs $1.50 (as of 2023).
You might have to pay this amount when mailing a letter or postcard to Canada.
Lettermail: Standard Size Mail
Suppose you plan to put a mailpiece in a special envelope or create a piece that will be folded to letter size. In that case, note the following size requirements for standard letters:
Lettermail Dimensions
| Dimension | Maximum | Minimum |
| Length | 11 1/2 inches | 5 inches |
| Thickness | 1/4 inch | 0.007 inch |
| Height | 6 1/8 inches | 3 1/2 inches |
Incentive Lettermail
Canada Post’s Lettermail™ is a convenient and affordable service to send items in Canada.
Examples of letter mail include the following:
- Letters, postcards, or self-mailers
- Annual, semi-annual, or quarterly reports
- Receipts or similar documents with financial information
- Notices of voting for provincial, federal, or municipal events
- CDs (compact discs) or DVDs (digital versatile discs)
- Dry biological specimens
- Flexible magnet
Taxes and Duties
Like most countries, Canada charges taxes and customs on imported goods.
The Goods and Services Tax (GST) is the first tax on imported products. It is a 5% federal tax levied on items sold to Canadian consumers for domestic use.
Some Canadian territories levy the HST (Harmonized Tax) to combine the provincial and general sales tax.
Additional Charges for Larger Mailpieces and Envelopes
Suppose your mailpiece exceeds its current rate’s maximum height, length, or thickness. In that case, USPS will charge you for its shipment at the next higher rate.
You will pay package rates for large envelopes that exceed the size limit.
Non-Standard and Oversize Mail
USPS’ maximum weight limit for mailpieces is 70lbs, and the maximum dimension (girth plus length) is 130 inches. USPS considers an item exceeding these requirements as nonmailable.
Say the nonmailable item is already in the postal network before USPS discovers it.
In that case, USPS may secure the package for pickup by the sender or recipient. These individuals will pay the oversized or overweight item fee of $100 before they can retrieve the item.
If the item remains unclaimed within 14 calendar days, USPS will usually abandon and dispose of it.
Weight, Size, and Shape Requirements
As mentioned above, USPS has established policies regarding mailpieces’ size, weight, and shape.
For example, a ¼ inch or less thick mailpiece must be rectangular. It must also be at least 5 inches (length) by 3 ½ inches (height).
Note: All mailpieces should be at least 0.007 inches thick.
Additionally, the maximum size for most items is 108 inches in combined girth and length.
Meanwhile, USPS Retail Ground items have a maximum dimension of 130 inches (girth plus length). However, you must pay oversized prices when shipping them.
On the other hand, some mail classes require lower weight limits. Still, the maximum mailable weight of any item is 70lbs.
How Many Stamps Do I Need for a Letter to Canada?
You can send as many stamps as you need to match the postage cost for shipping to Canada.
For example, customers generally send a 1oz letter (four sheets of standard printer paper and a business-sized envelope) or a postcard using one First-Class Mail Global Forever stamp. As of 2023, this stamp’s price is $1.50.
You can also use other stamps to send your letter to Canada. But the number of stamps you use should add up to $1.50.
Envelope Requirements
Here are the dimension requirements for sending large envelopes internationally:
- Minimum: 11 ½ inch (length) by 6 ⅛ inch (height)
- Maximum: 15 inches (length) by 12 inches (height)
- Thickness: Maximum thickness of ¾ inch
How to Weigh Your Envelope
During postage price calculation, USPS rounds up the parcel’s weight to the next pound for most weightier packages or the next available ounce rate for particular lightweight items.
This rule applies to all mail classes. For instance, if your package weighs 3lbs and 4oz, USPS will charge you at the 4lb-rate.
Sending More Than 3.5 Ounces to Canada or Large Envelopes to Canada
A standard letter’s maximum weight is 3.5oz, so use a flat (large envelope) when sending something weighing more than 3.5oz.
Where To Buy Stamps
You can purchase stamps from the following sources:
- Post offices: You can buy new stamps from USPS retail sites.
- USPS.com: You can browse and order stamps online through the Postal Service’s website.
- Pen pals: Find someone who likes to collect stamps and become pen pals.
- Vacationers: Ask your vacationing friends to mail you a postcard.
- Mailboxes: Many people get stamps daily. Ask friends and family to save them for you.
- Stamp dealers: You can buy vintage stamps from stamp dealers and collectors.
- The Internet: Some websites (other than USPS) sell stamps and stamp-collecting supplies.
- Grandparents and other relatives: Write to your relatives about stamp collecting. This initiative might make them happy, and they might write back using unique stamps.
- Trading: If you have multiple copies of the same stamp, you can swap them with a friend.
Buy Stamps Online
As mentioned, you can buy stamps online through USPS.com. But you can also purchase these mailing supplies from approved sellers like Stamps.com.
Stamp Prices for Letters and Postcards
You can use First-Class Mail International to send flats, letters, and postcards to foreign countries. The price for sending letters and postcards overseas is $1.50.
How Long Does It Take for Mail To Get to an Address in Canada?
Aside from pricing and procedures, you will likely consider how quickly mail arrives in Canada and whether you can track them while in transit.
The following sections explain the factors determining the speed of mail delivery in this vast nation.
Delivery Times for Letters to Canada
Here are the delivery times for various international services to give you an idea of how long it will take for your shipment to arrive in Canada:
- Priority Mail Express International: 3 to 5 business days
- Priority Mail International: 6 to 10 business days
- Global Express Guaranteed: 1 to 3 business days
- First-Class Mail International: Varies by destination
Can I Track Mail When It Moves Through Canada?
Priority Mail Express International, GXG, and Priority Mail International services include international tracking and insurance. You can track your mail if you use any of these products.
Sending Postage From the U.S. to Canada: How to Send a Letter From the USA to Canada
You’re probably excited to send your mail to your friend or loved one in Canada. But before you do so, consider these additional reminders about shipping postage from the U.S. to Canada:
Select a Method To Ship Your Mailpieces
When shipping internationally, choosing which mailing method suits you best is one of the first things to consider.
As shown above, USPS offers various international shipping services. These services differ in features and pricing.
Measure the Weight of Your Package
The costs of some shipping services depend on the package’s weight, so it is crucial to weigh your parcel before handing it over at the post office retail counter.
During postage price calculation for your parcel, USPS rounds up the weight to the next pound for many heavier packages or the next available ounce rate for lightweight ones.
This policy applies to domestic and international mail classes.
You can weigh your letter using a kitchen scale, self-service kiosk (SSK), postal scale, or at the post office counter.
Suppose your letter is bigger or heavier, your postcard is square or large, or you want to add services. In that case, you must pay extra.
Add-On the Special Services, if Required
You will pay additional fees if you want proof of delivery, signature services, insurance, or other optional features.
Here are two add-ons you can combine with your First-Class Mail International letter:
- Certificate of Mailing: This document proves that you sent an item from a post office location.
- Return Receipt: If you’re using a Registered Mail service, you can add this feature to your First-Class Mail International item.
USPS workers will attach a card to your item when you mail it from a post office.
The recipient will sign the card, and USPS will send it to you as a delivery record.
Note: Some countries will not require a recipient signature.
Buy and Employ Postage
You should buy and affix the appropriate number of stamps to your mail for postage.
As mentioned, you can send a one-ounce postcard or letter to any foreign country for just one Global Forever stamp.
However, if your letter weighs over one ounce, you can purchase more postage in the amount you need, up to 3.5oz.
Put stamps in the envelope’s upper right-hand corner. For postcards, you can affix the stamp in the space provided near the delivery address.
Write Sender Address
While the international address formats for each country differ, the delivery address should always be in English.
Write your return address (your address in the U.S.) in the top-left corner. Include these details on separate lines:
- Your complete name or company name
- Suite or apartment number
- Full street address
- City, State, and ZIP+4 Code
- USA
Note: ZIP+4 Codes are a more detailed version of the standard 5-digit ZIP codes, helping pinpoint delivery addresses within a ZIP code area.
Write Delivery Address
Write the recipient’s address on the envelope’s bottom center.
Generally, put the following information on separate lines:
- Recipient’s complete name or company name
- Street address
- City, subdivision (like state, province, or county), and postal code
- Country
Example of Canadian Address Format
Here’s an example of a Canadian address format:
- MR HENRY SAUNDERS
4383 Ross Street
Kingston ON K7M 7H6
On mail to Canada, put two spaces between the postal code and province abbreviation, as shown above between “ON” and “K7M 7H6”:
Use the standard two–character abbreviation for Canadian regions:
| Canadian Territories or Provinces | Postal Service Abbreviation |
| Alberta | AB |
| British Columbia | BC |
| Manitoba | MB |
| New Brunswick | NB |
| Newfoundland and Labrador | NL |
| Northwest Territories | NT |
| Nova Scotia | NS |
| Nunavut Territory | NU |
| Ontario | ON |
| Prince Edward Island | PE |
| Quebec | QC |
| Saskatchewan | SK |
| Yukon Territory | YT |
Mailing a Letter to Canada From the Post Office
After determining the postage rate that suits your budget and needs, you can select the mailing service accordingly.
Generally, if you want your package to arrive fast, you should pay more depending on the parcel’s size and weight.
How to Ship to Canada With USPS
USPS offers six different services for shipping international parcels. Pick from these services and follow the instructions.
Some services are restricted to specific countries or for particular types or amounts of content. Check the USPS’ Individual Country Listings for details regarding particular countries.
Check which services are available based on what you want to send and its destination. Then, fine-tune your decision based on speed, price, and available features.
COVID-19 or Coronavirus Status: Delivering Normally
USPS temporarily suspends global mail acceptance for specific locations due to issues related to the COVID-19 pandemic and other unforeseen service disruptions.
As of October 2023, avoid mailing items addressed to the places listed below until further notice:
- Afghanistan
- Belarus
- Brunei
- Laos
- Myanmar
- Niue
- Russia
- Sudan
- Syria
- Yemen
Tip
Consider comparing USPS services with other service providers’ offerings to determine which option is best for you.
Private carriers such as FedEx (Federal Express) and DHL (Dalsey, Hillblom, and Lynn) also offer international shipping.
Like USPS postage costs, FedEx and DHL pricing may depend on the package’s size, chosen delivery options, and destination.
Additional Information
Whether you choose a standard letter or “international flats,” you won’t go wrong with gathering as much info as possible when sending items internationally.
Consider the following details when shipping mail or packages to countries like Canada.
Mailing Restrictions and Prohibitions
USPS imposes specific standards and regulations for mailing prohibited, restricted, and hazardous materials, including smokeless tobacco and cigarettes.
You cannot send any of these items from the U.S. to any country:
- Air Bags
- Alcoholic Beverages
- Aerosols
- Dry Ice
- Hemp-based products (including CBD or cannabidiol)
- Marijuana
- Explosives
- Gasoline
Note: Flats and letters should only contain documents.
Shipping to a Military Post Office: FPO, APO, or DPO
You will pay domestic rates for parcels shipped to a military post office, including the following:
- FPO (Fleet Post Office)
- DPO (Diplomatic Post Office)
- APO (Army or Air Force Post Office)
However, these sites require customs forms and impose specific restrictions.
For Businesses
USPS offers cost-effective services so businesses can grow their network and thrive in the ever-growing global market.
For example, USPS’ free global shipping software can provide business owners with a data file containing shipment processing details and tracking information.
Postal Code H0H 0H0
Every year, during Christmas, many children write letters to Santa Claus to let him know how good they’ve been and what they want for Christmas.
The problem is that people do not know where to send them. Canada resolved this issue by creating an official postal code for Santa Claus: H0H 0H0.
FAQs
How many stamps do I need for a large envelope (flats) to Canada?
The answer to this question depends on what you want to send and where to send it.
Postage costs for large envelopes or flats weighing up to 15.994oz vary depending on the mailpiece’s weight and destination, starting from $3.
Are there prohibited items I shouldn’t mail to Canada?
Yes. As shown above, USPS imposes rules regarding prohibited or restricted items.
You cannot and should not ship any of the following items to Canada:
- Poisonous or infectious substances
- Chain letters and other documents supporting fraudulent schemes
- Corrosives
- Obscene or indecent materials
Does mail to Canada have to go through customs?
Yes. Any mail sent via USPS will go through U.S. Customs and the CBSA (Canadian Border Services Agency).
What happens if a mail to Canada is incorrectly addressed?
The local post office typically handles mailpieces that are addressed incorrectly and need a return address. USPS may also transfer these items to the Mail Recovery Center.
Can I use two Forever stamps for international postage?
You can if the number of your Forever Stamps doesn’t match the cost of your postage.
You can use Forever Stamps for shipping overseas. However, you usually have to attach additional postage because international prices are higher than domestic prices.
A Forever Stamp’s value equals the domestic First-Class Mail letter rate on the day of use.
Can I mail a letter to Canada using Forever stamps?
Yes. As shown above, USPS offers a Global Forever stamp to ship mail or packages overseas, including Canada.
How many stamps do I need to buy for a postcard?
If you’re mailing a postcard to Canada, you should buy and use one Global Forever Stamp for $1.50.
Check the USPS website for various stamps to buy and info regarding current postage rates and policies.
Will my mail go through customs?
If your mail comes from abroad, it will likely go through customs. Sometimes, a message will indicate that your package is “Processing Through Facility” or “Released From Customs.”
However, you may also see a generic “In Transit” message in your tracking information.
References
- USPS Shipping to Canada from the US
https://www.stamps.com/usps/shipping-to-canada/ - How to Send a Letter or Postcard: International
https://www.usps.com/international/letters.htm - Global: Poinsettia Stamps
https://store.usps.com/store/product/buy-stamps/global-poinsettia-stamps-S_565904 - Lettermail
https://www.canadapost-postescanada.ca/cpc/en/support/articles/lettermail/overview.page - First-Class Mail International
https://www.usps.com/international/first-class-mail-international.htm - First-Class Package International Service
https://www.usps.com/international/first-class-package-international-service.htm - What Is Global Express Guaranteed
https://faq.usps.com/s/article/What-Is-Global-Express-Guaranteed - What is Priority Mail Express International
https://faq.usps.com/s/article/What-is-Priority-Mail-Express-International - Mailing & Shipping Prices
https://www.usps.com/business/prices.htm - Priority Mail International
https://www.usps.com/international/priority-mail-international.htm - USPS Priority Mail International
https://www.stamps.com/usps/priority-mail-international/ - How to Use the USPS Shipping Calculator
https://www.stamps.com/calculators/how-to-use-usps-shipping-calculator/ - Extra Services
https://pe.usps.com/businessmail101?ViewName=ExtraServices - Registered Mail
https://www.uspsoig.gov/reports/audit-reports/registered-mail - Click-N-Ship® – The Basics
https://faq.usps.com/s/article/Click-N-Ship-The-Basics - 2023 Mail/Shipping Rates
https://stamps.custhelp.com/app/answers/detail/a_id/7558/~/2023-mail%2Fshipping-rates - International Mail & Shipping Services
https://www.usps.com/international/mail-shipping-services.htm - Postage Stamp Price Increase
https://www.stamps.com/usps/postage-rate-increase/ - Sizes for Letters
https://pe.usps.com/businessmail101?ViewName=Letters - Commercial Mail Customer Guide
https://www.canadapost-postescanada.ca/cpc/doc/en/support/customer-guide/commercial-mail.pdf - Parcel Size, Weight & Fee Standards
https://faq.usps.com/s/article/Parcel-Size-Weight-Fee-Standards - Minimum and Maximum Sizes
https://pe.usps.com/businessmail101?ViewName=MinMax - How to Send a Letter or Postcard: International
https://www.usps.com/international/letters.htm - What Are You Mailing? International
https://pe.usps.com/text/dmm100/mailing-international.htm - Automated Package Verification
https://www.usps.com/business/verify-postage.htm - Where to Get Stamps
https://about.usps.com/publications/pub192/pub192_004.htm - U.S. Postal Service Approval
https://www.stamps.com/company-info/usps/ - Mailing & Shipping Prices
https://www.usps.com/business/prices.htm - A32 Canada Only
https://pe.usps.com/text/pub28/28apa_005.htm - International Shipping Restrictions, Prohibitions, & HAZMAT
https://www.usps.com/international/shipping-restrictions.htm - How is Undeliverable and Misdelivered Mail Handled?
https://faq.usps.com/s/article/How-is-Undeliverable-and-Misdelivered-Mail-Handled - Forever Stamp Fact Sheet
https://about.usps.com/news/fact-sheets/forever-stamp-facts.htm