According to the U.S. Postal Service (USPS), you are not allowed to ship any combustible liquids internationally, only through domestic mail. A combustible liquid must also meet three requirements before it can be considered safe for domestic shipping. Its flash point will determine whether the package qualifies as "Other Regulated Materials-Domestic" (ORM-D) material. You must package the perfume oil by USPS standards and then label it correctly before shipping.
Before the shipping process can even begin, the perfume oil must first be classified by its flash point. Flash point determines whether the perfume oil can ignite in air and what the minimal temperature point is that will cause this to occur. You have to ship perfume oils that ignite at 100 degrees or more with a filed HAZMAT certificate through USPS. The reason that flash point is so important is because, when packages fly, there is natural air decompression--this can cause the bottles of perfume oil to explode.
To package the perfume oil, you must make sure that the amount being shipped weighs no more than one gallon per box. You must also pack the perfume oil in a metal container within the box. Ample bubble wrap or filler must be added to stabilize the items in the box and to try to prevent possible leakage. This must be contained in a box large enough to fit the items within it. A stronger outer box must then be used to put the smaller box within. This is an extra measure of protection against fire.
Once the perfume oil is safely and securely packaged, the label must be properly marked by the USPS either online or in person. ORM-D must appear on the label to define whether the package may be shipped by air or by ground. According to USPS, ORM stands for Other Regulated Material and is considered a consumer commodity.