By airmail is often used to describe sending a letter or package via air transportation. However, there are various synonyms that can be used to convey the same meaning. For example, you could use the phrase "by air delivery" or "by air shipment" to indicate that your package will be arriving via airplane. Other phrases, such as "airborne delivery" or "airmail service" can also be used to describe the method of delivery. Additionally, you could use specific terms depending on the type of package or document being sent, such as "air courier" or "airfreight." Regardless of the term used, sending items by air is often preferred for its speed and efficiency.