Mail Slot Installation Glass Door? The 48 Correct Answer

roadside mailboxes

Mailbox size and construction standards

A mailbox with the Postmaster General’s (PMG) seal of approval conforms to USPS size and construction standards. If you build your own mailbox or buy a custom one, it must meet PMG standards. Show your mailbox plans or custom box to your local postmaster for approval.

For drawings and dimensions for building your own mailbox, write to US Postal Service Engineering.

Would you like to buy a mailbox big enough for parcels? See Next Generation Mailboxes.

Post boxes, also known as post boxes, can be placed on outside walls and front doors so you no longer have to go to the post box to get your mail. Mail slots feature flaps or moveable panels that block drafts, and decorative mail slots come in a variety of colors, from bright brass to copper. The slot cover can be embossed with your initials or words like “Mail” or “Letters” and a delicate design all around for an elegant antique look.

Disclosure: We may receive commissions for purchases made through links in this post.

Insulating a mailbox might not be something you think about on a regular basis. It’s common to assume that these slits are so small that they’re not worth isolating, but that’s not necessarily true. So how do you insulate a mail slot? And what materials can you use? We’ve researched the best ways to do this.

Here are some ways you can isolate your mail slot:

Seal and caulk the edges of the slit. Use insulating foam. Attach sealing strips. Install a mail slot cover. Install a DIY insulation material

Insulating your letterbox can help prevent cool air from entering your home. It can also prevent warm air in your home from escaping outside, keeping the inside cooler than you want. Read on to learn more about how to effectively isolate your mailbox.

Ways to isolate a mail slot

Before isolating your mailslot, make sure the slot is installed correctly. This means that there are no cracks and gaps between the slot and the door and that all screws are tightened and securely fastened to the top and bottom.

1. Seal and caulk the edges of the slit

Insulating your mail slot can help prevent unwanted drafts and air leaks near the door area. If the slit has any holes or tears around it, it will be fairly easy for air to enter through the opening.

The vent itself, even when closed, offers a chance for cold air to enter your home and warm air to escape – although we’ll get to how to insulate this area in a moment.

However, one of the best ways to reduce this is to properly caulk and caulk the edges of the slit. The easiest way to do this is to run your hand around the perimeter of the slit and feel for cold drafts.

You may also be able to visually identify holes in the space between the sides of the slot and the door. If you do, take your sealer or caulk and apply it to those areas. Be sure to wipe the area with a cleaning solution and dry completely for the caulk to bond properly.

Click here to see this seal on Amazon.

2. Use insulation foam

You can also use expanding and non-expanding foam insulation to keep air from entering your home.

If your mail slot fits properly around the door, expanding foam may not be necessary. In this case, the non-expanding foam may be better. Apply the foam to all four sides of the slit to keep warm air inside in winter (or cold air in summer).

Click here to see this insulation foam on Amazon.

3. Attach sealing strips

Another easy way to insulate your mail slot is to add weatherstrips. Weatherstripping strips are affordable, readily available, and easy to use on a variety of surfaces. You can purchase weatherstrips made of open-cell foam, felt, vinyl, or various types of metal.

However, you may want to use a softer material like felt or foam so that the mail slot flap isn’t difficult to open.

Weatherstrips are usually supplied with a self-adhesive backing and can be fitted once cut to size. Felt caulking strips can be particularly beneficial as they are usually thicker and denser – not to mention they are usually cheaper.

However, vinyl weatherstrips are more durable and resistant to moisture, which is great if you put them on the outside of the slot. So, for example, if you are replacing the weather strip on the outside of the slot, rubber or vinyl may be ideal, while felt is better for the inside.

Click here to see this weather protection on Amazon.

4. Install a mail slot cover

Another option is to attach a cover to the outside of the mail slot. Mail slot covers prevent drafts and precipitation from seeping through the mail slot, which is perfect for extreme weather conditions.

You can also increase their efficiency by adding another layer of thin insulation (e.g. weatherstripping) between the cover and the top of the letterbox housing.

They are also helpful in preventing possible intrusion by burglars and mail thieves by making access more difficult. You can find these covers at your local hardware store or online and have them installed in minutes.

Click here to view this mail slot cover on Amazon.

5. Install a DIY insulation material

You can also use materials such as heavy pieces of curtains, old comforters, or blankets to insulate the back of the letterbox flap. Basically, you can use any dense, thin fabric to insulate the mail slot.

However, it is best to use these materials on the inside of the flap to prevent them from getting wet from moisture from the outside. It is also best to use them in conjunction with an outer slot cover on the outside to prevent water and precipitation from reaching them.

How tall should mail slots be?

Most mail slots in the US average about 30-40 inches off the ground. This height makes it easier for postal workers to simply slide mail through the slot without having to bend too low.

Is a mail slot in the door secure?

Mail slots on doors can pose a significant hazard when it comes to gaining entry into your home. For example, would-be thieves can simply slide a cord or hook wire down the slide to unlock the door and gain entry into your home.

However, there are ways to prevent this and secure the mailslot without removing it entirely. Here are a few tips on how to do it:

Install a mail slot cover

One of the quickest ways to make your mail slots less attractive to burglars is to simply cover them up. Mail slot covers can be purchased at a local hardware store and then drilled into the door to cover the mail slot.

There are different types of covers to choose from, but if you live in an area with extreme weather conditions, it’s best to choose one made of insulating, weather-friendly materials like vinyl or rubber.

Install a second latch

Installing a mail slot in your door creates a hole that can weaken the integrity of the door. This makes the door easier to kick in in the event of a break-in. One way to prevent this is to install a second latch.

Another deadbolt can help provide protection and support if a burglar tries to break into the door. When shopping for bars, look for ones with consistent customer reviews and impressive safety standards.

Click here to see this bar on Amazon.

Install an air outlet diverter

You can usually find air deflectors on the side or back of a home’s foundation. These are used to bleed air from household dryers and other equipment. Surprisingly, they are also a great deterrent when it comes to protecting mailboxes from burglars.

This is an effective and relatively inexpensive way to prevent a burglar from easily sliding their hand into your mail slot and reaching up to access the lock. You can install the air vent diverter in as little as 15 minutes and can find it at local hardware stores and online.

Click here to see this air outlet diverter on Amazon.

Can a letter slot be built into a glass door?

It’s very unlikely that you’ll find a glass door that has a mail slot built right into the glass part. It’s also extremely difficult to cut into a glass door without breaking it – unless you have special tools designed for this type of job.

The best way to get a mail slot in a glass door is to purchase a door that has a metal or wood partition in the middle or at the bottom. You can install the mail slot in this part of the door.

You can often find glass doors that already have these dividers and also include mail slots. You will often see these in professional buildings.

Are mail slots a standard size?

Mail slots in the US are typically around 9 inches wide and 3 inches long. This slot size is large enough to accommodate standard letter and magazine sizes. However, you can find custom slots that are larger.

pack things

We hope this post has helped illustrate the different ways you can isolate your mail slot. Remember that it is best to use waterproof materials when insulating the outside of the slot.

Before you go, be sure to check out these other posts:

R13 Insulation: Uses, Thickness, Cost and More

Does yellow insulation contain fiberglass?

How to Buy and Install a Wall Mail Slot Post Box

A wall unit mail slot offers the ultimate convenience for homeowners lucky enough to still get mail delivered.

When installing a wall mailbox, you can choose between:

Door Mounted – A nostalgic door letterbox can be installed through a front (or garage) door.

THROUGH THE WALL – Your wall mounted mailbox can be installed through the wall of your home.

An outer letterbox cover (or lid) covers the letterbox, keeping the home insulated from the elements. USPS mailbox regulations require that horizontal letterboxes be hinged at the top and vertical letterboxes at the opposite side of the door hinges (when mounted on a door).

When the postman approaches the house, the postman simply lifts the lid of the letterboxes in residential buildings to introduce the mail. Mail goes through your door (or the wall in the case of wall-mounted door slots) and is safely inside your home, either on the floor or in a mailbox.

Benefits of a Residential Mail Drop Slot

While residential letterboxes are only advisable for postal areas with walk-up delivery, these through-wall and through-door mailboxes offer triple advantages:

Mailboxes in private homes are often far more secure than non-lockable post or wall mounted mailboxes. Mail slots are less expensive. Mail slots do not require the homeowner to leave their home to retrieve their mail.

For disabled people or elderly people with reduced mobility, this third benefit of slotted mailboxes is undoubtedly the most significant, as their mail can be collected safely and conveniently from their homes.

Ordering a mailbox

When shopping for home mailboxes, take the time to consider these three factors:

Letter slot size Letter slot design Whether or not you want to equip your letter box with a collection box for indoor use

Mail slot size

The size of your installed mailbox should be large enough to hold large envelopes, magazine subscriptions, or small packages, and per USPS mailbox requirements, the mailbox should be at least 1 ½ x 7 inches.

Mail Slot Completion

The finish of your mail slot should match or complement the finish of your door or wall hardware. For example, if you have doorway hardware with a brass finish with a natural patina, you should choose a brass letter slot with a natural patina finish, or consider a strong contrast to that brass finish to avoid surface clashing.

Mail Slot Accessory

If scattering your mail over a high traffic floor area is a safety concern, an indoor mail collection box accessory or a simple indoor letter basket is advisable. In addition, indoor mail collection accessories are also recommended when the floor surface (e.g. softwood floors) is easily damaged by the regular delivery of parcels or parcels that could scratch or damage them.

Reinstallation Considerations

Investing the time to consider these three factors can also increase the success of installing your mail slot in a new location:

Check with your postmaster Ensure mail slot height is correct Consider installing an inner hood

Contact your postmaster

First, check with your local postmaster to make sure your wall letterbox is a viable option for mail delivery to your home. While a trip to any of the major cities in Europe and many of the major cities on the east coast of North America will quickly confirm the popularity of letterboxes (in Europe they are called mailboxes), letterboxes are less common in the vast majority of North America. So before you buy a letterbox for your home, take the time to make sure mail delivery to your area is available.

Correct the mailbox height

Second, the USPS requires the bottom of your private mail slot to be at least 30 inches off the ground after installation. Although the USPS does not specify a height restriction, it is advisable to mount the mail slot at a height that will allow the mailman to easily deliver your mail without reaching up or bending too low.

Installation of the inner hood

In addition, to ensure mail flows smoothly through the mail slot upon delivery, the USPS requires that if an inner privacy hood is used, the hooded portion should not be below the bottom of the outer panel at the horizontal mail slot. For vertical letter trays, the hood should not protrude beyond the side of the outer panel on the door hinge side. Finally, the inner privacy hood should not extend more than 2 1/16 inches past the inside of the door, regardless of orientation.

Mail Slot Marks

To shop the largest inventory of residential wall mounted mailboxes, browse the selection at The MailboxWorks, North America’s largest retailer of all types of mailboxes – commercial and residential.

Auth Florence Mail Slots

The MailboxWorks features the elegantly simple aluminum letter slot designed by Auth Florence and meets all USPS letter slot regulations. Florence mail slots are available in eleven beautiful powder coated finishes including antique copper, antique bronze, black, gold, silver stain and more. In addition, Florence mail slots are offered with optional engraving on the mail slot door, allowing homeowners to have their address or name engraved directly in their mail slot.

European home mail slots

The MailboxWorks also offers a European Home mail slot that resonates with a strong modern contemporary design taste. These corrosion-resistant stainless steel mail slots are handcrafted with a stunning satin finish and meet all USPS standards. Order your letterbox with mail collection box for a complete letterbox system.

Streetscape mail slots

In addition, The MailboxWorks also features a Streetscape Executive mail slot, handcrafted by artisans in the USA. Streetscape Executive letter slots also meet USPS standards and feature a unique patinated brass finish that requires no maintenance. No two of these brass mail slots are alike and all feature a solid brass internal mail chute to channel mail delivery. Additionally, your brass house numbers can be custom welded to the letterbox door to further customize your letterbox.

Read all of our articles on mail slots including:

Do you have anymore questions?

If you still have questions about mailslot mailboxes, please contact our mailbox experts by calling The MailboxWorks toll-free at 1-866-717-4943. You can also contact us online or email us.

Categorized in: DIY Mailbox Installation & Upgrades

Door Slots vs. Traditional Mailboxes: Which is Better?

Contrary to what some people believe, the United States Postal Service (USPS) does not require every home or apartment building to have a traditional mailbox. An alternate form of receiving mail permitted by the USPS is through a door slot. As shown below, a door slot is a rectangular hole into which a Mall is inserted. The postman can push the tenants’ mail into the slot, after which it will fall on the ground or in a bucket in the tenants’ house. So which of these email delivery solutions work best?

Door slots do not support outgoing email

While both traditional letterboxes and door slots allow mail to be received, only traditional letterboxes support outgoing mail. The one-way design of the door slots allows tenants to receive mail but cannot send mail. If a tenant needs to mail a letter, he or she must take it to the local post office. In comparison, traditional mailboxes allow tenants to send mail by placing their stamped letters in the mailbox and raising the carrier flag. When the carrier flag is raised, postmen know the mailbox has outbound mail.

Door slots are time consuming for postal couriers

Delivering mail to door slots is time consuming for postal couriers. When a neighborhood or condominium uses door slots, mail couriers must go to each house to deliver that unit’s mail. It is a tedious task that wastes a lot of time. On the other hand, if a neighborhood or shared flat uses roadside mailboxes, postmen can simply drive past the mailboxes without getting out of their vehicle.

Of course, neighborhoods and shared flats can use some form of central mail delivery instead of roadside mailboxes. STD-4C Mailboxes and Cluster Box Units (CBU) offer an even faster and more streamlined approach to mail delivery.

Door slits cost the USPS money

Because they are time consuming for mail couriers, the USPS spends more money delivering mail to these containers than to traditional mailboxes. According to the USPS Office of Inspector General, the USPS spends $353 per household per year to deliver mail to your door. However, the USPS only spends $224 per household per year to deliver mail to curbside mailboxes, and it only spends $160 per household or year to deliver mail to a centralized mail delivery solution such as STD-4C mailboxes or to deliver CBUs.

About Forsite:

Welcome to Forsite! You’ve found your best source for custom street signs and wayfinding. We manufacture and install upscale site facilities throughout the United States.

Forsite can provide all your signage needs for your Master Planned Community or Residential Development. We help our clients create a unified, upscale look and increase property value by ‘bundling’ themed packages of decorative street signage, mailboxes, pole and wall lighting, and wayfinding.

You can count on the experts at Forsite to improve the quality of your community today. Contact us today to get started by speaking to one of our experienced team members at 855-537-0200.

Free Ground Shipping in the contiguous 48 United States on orders over $100.

Not the door mailbox you are looking for? Check out our full range of mail slots for your door or wall.

This large mail slot is available in five finish options. The dimensions of the actual mail slot are 3.625″H x 13″W ​​x 1 ¾”D and the actual opening through which mail passes is 2″H x 11″W. When your mailman brings mail to your door, you can dress Up your mail slot with a new brass door slot This door slot consists of two main parts, the inside of the letter slot & the outside of the letter slot and they are screwed to the door separately with wood screws.

Looking for a smaller door mailbox? Check out the letter slot with sleeve option for your wood or metal door.

A sleeve for hollow doors is available as an option. The sleeve is made of stainless steel and is designed for standard doors with a thickness of 1 ¾. The outer flap on the door slot is spring-loaded to automatically close when opened, the inner flap is not. That is, there is both an inner cover (door flap) and an outer cover (door flap).

Use above option to add receiving pocket Mail Catcher For Mail Slots. No tools required to install the bag. It’s easy to install to intercept your mail. No need to keep a basket or trash can under your mail slot hoping it will catch the mail as it falls through your mail slot. The optional mailbox pocket works with all standard size horizontal mailboxes, up to 11″ wide and 4″ high. The overall size of the mail bag is 21.8″H x 16.2″W x 0.5″D. Quick and easy to install.

The 6 finish options are: Brass, Antique Brass, Oiled Bronze, Satin Nickel and Lifetime PVD Brass. The PVD brass finish is a lifetime plating specially formulated to withstand rough treatment or saltwater air.

Large Magazine Mail Slot SPECIFICATIONS AND FEATURES

Drill pilot holes for the outer and inner mail slot faceplates on the door. If the manufacturer provided a template, use the marks you made when marking the template on the door. If a template was not provided, hold the panels against the door over the hole you cut and mark the screw holes on either side of the door. Vinyl, aluminum, and steel doors are 2 inches thick, but wood doors with recessed sections may be too thin to mount panels on either side of the door. If this is the case with your door, only fit the outside sign.

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Door Slots vs. Traditional Mailboxes: Which is Better?

Contrary to what some people believe, the United States Postal Service (USPS) does not require every home or apartment building to have a traditional mailbox. An alternate form of receiving mail permitted by the USPS is through a door slot. As shown below, a door slot is a rectangular hole into which a Mall is inserted. The postman can push the tenants’ mail into the slot, after which it will fall on the ground or in a bucket in the tenants’ house. So which of these email delivery solutions work best?

Door slots do not support outgoing email

While both traditional letterboxes and door slots allow mail to be received, only traditional letterboxes support outgoing mail. The one-way design of the door slots allows tenants to receive mail but cannot send mail. If a tenant needs to mail a letter, he or she must take it to the local post office. In comparison, traditional mailboxes allow tenants to send mail by placing their stamped letters in the mailbox and raising the carrier flag. When the carrier flag is raised, postmen know the mailbox has outbound mail.

Door slots are time consuming for postal couriers

Delivering mail to door slots is time consuming for postal couriers. When a neighborhood or condominium uses door slots, mail couriers must go to each house to deliver that unit’s mail. It is a tedious task that wastes a lot of time. On the other hand, if a neighborhood or shared flat uses roadside mailboxes, postmen can simply drive past the mailboxes without getting out of their vehicle.

Of course, neighborhoods and shared flats can use some form of central mail delivery instead of roadside mailboxes. STD-4C Mailboxes and Cluster Box Units (CBU) offer an even faster and more streamlined approach to mail delivery.

Door slits cost the USPS money

Because they are time consuming for mail couriers, the USPS spends more money delivering mail to these containers than to traditional mailboxes. According to the USPS Office of Inspector General, the USPS spends $353 per household per year to deliver mail to your door. However, the USPS only spends $224 per household per year to deliver mail to curbside mailboxes, and it only spends $160 per household or year to deliver mail to a centralized mail delivery solution such as STD-4C mailboxes or to deliver CBUs.

About Forsite:

Welcome to Forsite! You’ve found your best source for custom street signs and wayfinding. We manufacture and install upscale site facilities throughout the United States.

Forsite can provide all your signage needs for your Master Planned Community or Residential Development. We help our clients create a unified, upscale look and increase property value by ‘bundling’ themed packages of decorative street signage, mailboxes, pole and wall lighting, and wayfinding.

You can count on the experts at Forsite to improve the quality of your community today. Contact us today to get started by speaking to one of our experienced team members at 855-537-0200.

Enter the characters you see below

Sorry, we just need to make sure you’re not a robot. For best results please make sure your browser accepts cookies.

Disclosure: We may receive commissions for purchases made through links in this post.

Insulating a mailbox might not be something you think about on a regular basis. It’s common to assume that these slits are so small that they’re not worth isolating, but that’s not necessarily true. So how do you insulate a mail slot? And what materials can you use? We’ve researched the best ways to do this.

Here are some ways you can isolate your mail slot:

Seal and caulk the edges of the slit. Use insulating foam. Attach sealing strips. Install a mail slot cover. Install a DIY insulation material

Insulating your letterbox can help prevent cool air from entering your home. It can also prevent warm air in your home from escaping outside, keeping the inside cooler than you want. Read on to learn more about how to effectively isolate your mailbox.

Ways to isolate a mail slot

Before isolating your mailslot, make sure the slot is installed correctly. This means that there are no cracks and gaps between the slot and the door and that all screws are tightened and securely fastened to the top and bottom.

1. Seal and caulk the edges of the slit

Insulating your mail slot can help prevent unwanted drafts and air leaks near the door area. If the slit has any holes or tears around it, it will be fairly easy for air to enter through the opening.

The vent itself, even when closed, offers a chance for cold air to enter your home and warm air to escape – although we’ll get to how to insulate this area in a moment.

However, one of the best ways to reduce this is to properly caulk and caulk the edges of the slit. The easiest way to do this is to run your hand around the perimeter of the slit and feel for cold drafts.

You may also be able to visually identify holes in the space between the sides of the slot and the door. If you do, take your sealer or caulk and apply it to those areas. Be sure to wipe the area with a cleaning solution and dry completely for the caulk to bond properly.

Click here to see this seal on Amazon.

2. Use insulation foam

You can also use expanding and non-expanding foam insulation to keep air from entering your home.

If your mail slot fits properly around the door, expanding foam may not be necessary. In this case, the non-expanding foam may be better. Apply the foam to all four sides of the slit to keep warm air inside in winter (or cold air in summer).

Click here to see this insulation foam on Amazon.

3. Attach sealing strips

Another easy way to insulate your mail slot is to add weatherstrips. Weatherstripping strips are affordable, readily available, and easy to use on a variety of surfaces. You can purchase weatherstrips made of open-cell foam, felt, vinyl, or various types of metal.

However, you may want to use a softer material like felt or foam so that the mail slot flap isn’t difficult to open.

Weatherstrips are usually supplied with a self-adhesive backing and can be fitted once cut to size. Felt caulking strips can be particularly beneficial as they are usually thicker and denser – not to mention they are usually cheaper.

However, vinyl weatherstrips are more durable and resistant to moisture, which is great if you put them on the outside of the slot. So, for example, if you are replacing the weather strip on the outside of the slot, rubber or vinyl may be ideal, while felt is better for the inside.

Click here to see this weather protection on Amazon.

4. Install a mail slot cover

Another option is to attach a cover to the outside of the mail slot. Mail slot covers prevent drafts and precipitation from seeping through the mail slot, which is perfect for extreme weather conditions.

You can also increase their efficiency by adding another layer of thin insulation (e.g. weatherstripping) between the cover and the top of the letterbox housing.

They are also helpful in preventing possible intrusion by burglars and mail thieves by making access more difficult. You can find these covers at your local hardware store or online and have them installed in minutes.

Click here to view this mail slot cover on Amazon.

5. Install a DIY insulation material

You can also use materials such as heavy pieces of curtains, old comforters, or blankets to insulate the back of the letterbox flap. Basically, you can use any dense, thin fabric to insulate the mail slot.

However, it is best to use these materials on the inside of the flap to prevent them from getting wet from moisture from the outside. It is also best to use them in conjunction with an outer slot cover on the outside to prevent water and precipitation from reaching them.

How tall should mail slots be?

Most mail slots in the US average about 30-40 inches off the ground. This height makes it easier for postal workers to simply slide mail through the slot without having to bend too low.

Is a mail slot in the door secure?

Mail slots on doors can pose a significant hazard when it comes to gaining entry into your home. For example, would-be thieves can simply slide a cord or hook wire down the slide to unlock the door and gain entry into your home.

However, there are ways to prevent this and secure the mailslot without removing it entirely. Here are a few tips on how to do it:

Install a mail slot cover

One of the quickest ways to make your mail slots less attractive to burglars is to simply cover them up. Mail slot covers can be purchased at a local hardware store and then drilled into the door to cover the mail slot.

There are different types of covers to choose from, but if you live in an area with extreme weather conditions, it’s best to choose one made of insulating, weather-friendly materials like vinyl or rubber.

Install a second latch

Installing a mail slot in your door creates a hole that can weaken the integrity of the door. This makes the door easier to kick in in the event of a break-in. One way to prevent this is to install a second latch.

Another deadbolt can help provide protection and support if a burglar tries to break into the door. When shopping for bars, look for ones with consistent customer reviews and impressive safety standards.

Click here to see this bar on Amazon.

Install an air outlet diverter

You can usually find air deflectors on the side or back of a home’s foundation. These are used to bleed air from household dryers and other equipment. Surprisingly, they are also a great deterrent when it comes to protecting mailboxes from burglars.

This is an effective and relatively inexpensive way to prevent a burglar from easily sliding their hand into your mail slot and reaching up to access the lock. You can install the air vent diverter in as little as 15 minutes and can find it at local hardware stores and online.

Click here to see this air outlet diverter on Amazon.

Can a letter slot be built into a glass door?

It’s very unlikely that you’ll find a glass door that has a mail slot built right into the glass part. It’s also extremely difficult to cut into a glass door without breaking it – unless you have special tools designed for this type of job.

The best way to get a mail slot in a glass door is to purchase a door that has a metal or wood partition in the middle or at the bottom. You can install the mail slot in this part of the door.

You can often find glass doors that already have these dividers and also include mail slots. You will often see these in professional buildings.

Are mail slots a standard size?

Mail slots in the US are typically around 9 inches wide and 3 inches long. This slot size is large enough to accommodate standard letter and magazine sizes. However, you can find custom slots that are larger.

pack things

We hope this post has helped illustrate the different ways you can isolate your mail slot. Remember that it is best to use waterproof materials when insulating the outside of the slot.

Before you go, be sure to check out these other posts:

R13 Insulation: Uses, Thickness, Cost and More

Does yellow insulation contain fiberglass?

Envelopes must be rectangular and made of paper to qualify for mail rates. Your envelope must be a maximum of 11-1/2″ long x 6-1/8″ high. (A standard #10 envelope is 9-1/2 inches long x 4-1/8 inches high.) You can fold what you put in your envelope, but it must stay flat — no thicker than 1/4 inch .

If you want to mail letter-size paper without folding it, you can use a large envelope (called a “flat” envelope); postage for apartments starts at $1.20. If your large envelope is not square, rigid (cannot be bent), or lumpy (not uniform thickness), you need to pay the package price.

TIP: If your envelope does not fit through USPS mailing machines, or is stiff, lumpy, or has clasps, strings, or buttons, it is “unworkable” and you will have to pay an additional $0.39 to ship it. (See additional postage in step 3.) You will also have to pay more if your envelopes are square or vertical (higher than wide).

Postcards are short messages that you don’t need to put in an envelope. Save money with a $0.44 postcard stamp to send a standard size postcard anywhere in the US. and are between 0.007″ and 0.016″ thick.