The USPS moves millions of letters and packages every day, and for most people, mailing something is as simple as putting it in a box, adding postage, and sending it on its way. Because the process seems so straightforward, it’s easy to assume almost anything can be mailed without a problem.

That’s not always the case.

Some everyday items are restricted because they create safety concerns during transport. Others are frequent targets for theft or can cause issues if they’re damaged in transit. In some cases, federal regulations simply don’t allow them to be shipped through the mail.

Before you seal up your next package, it’s worth knowing which items deserve a second look. Here are some common things that can create problems if you send them through USPS.

Cash and Gift Cards

Sending cash through the mail is always a gamble. If an envelope is lost or stolen, recovering the money is extremely difficult.

Gift cards carry many of the same risks. Since they’re often as good as cash, they can be attractive targets for thieves if discovered during transit.

Checks

For years, mailing checks was routine. Today, many people are more cautious because of mail theft and check fraud.

Criminals can steal checks, alter the information, and attempt to cash or deposit them. Electronic payments are often a safer option whenever they’re available.

Ammunition

Ammunition cannot be sent through USPS.

Because it contains explosive components, it presents obvious safety concerns during handling and transportation. Attempting to mail ammunition can result in penalties and legal issues.

Alcohol

A bottle of wine or a favorite craft beer may seem like a thoughtful gift, but USPS generally does not allow alcohol shipments.

Federal postal regulations prohibit mailing alcoholic beverages unless very specific licensing requirements are met.

Pets

Most household pets cannot be mailed.

Cats, dogs, and other common companion animals require proper care, food, water, and monitoring during travel. Standard mail services aren’t equipped to provide those needs, which is why shipping restrictions exist.

Marijuana

Even in states where marijuana is legal, mailing it through USPS remains illegal under federal law.

Certain hemp products may qualify for shipment if they meet federal requirements, but marijuana itself is prohibited.

Fireworks

Fireworks are completely banned from the mail system.

The risk of fire or explosion makes them unsafe for transportation through standard postal channels, regardless of size.

Traditional Thermometers

Older thermometers often contain mercury, a toxic substance that can create serious health and environmental concerns if released.

Because breakage is always possible during shipping, these items face strict mailing restrictions.

Perfume

Many people are surprised to learn that perfume can be difficult to ship.

Most fragrances contain alcohol, which makes them flammable. That means they may be subject to special packaging, labeling, and transportation requirements.

Nail Polish

Nail polish falls into a similar category.

The chemicals that give it its consistency also make it flammable. Shipping it often requires following specific rules that don’t apply to ordinary household items.

Hand Sanitizer

Hand sanitizer became a household staple in recent years, but many formulas contain high amounts of alcohol.

That flammable content places it under hazardous-material guidelines, which can limit how it may be shipped and transported.

Items Containing Mercury

Mercury isn’t limited to old thermometers.

Certain barometers, switches, medical devices, and specialty equipment may also contain it. If these items break during transit, they can release toxic materials that create health and safety risks for postal workers and recipients alike.

Mailing a package may seem simple, but some items require extra attention before they’re sent. A quick check of USPS regulations can help you avoid delays, rejected shipments, lost money, or unexpected headaches later on.