Submitting music to a radio station involves addressing it to the right person and sending it in the format that they are familiar with, along with supporting documentation. This involves some research and contact before the music is sent to find out the name of the right person and what they expect. Typically, the person in a radio station that receives and listens to new music is the music director.
The main formats that music directors will receive are streamed digital tracks and CD's. If the artist is sending the song or album digitally, it is not recommended that it is sent in a way that has to be downloaded by the recipient, particularly if the artist is not familiar to the radio station. It is much more trustworthy to send it using a well-known streaming service. There are also specialist services, although they often cost money. An example of this is DMDS, or Digital Music Delivery Service.
If the artist is sending the music by CD it is recommended that the CD is sent in a hard case rather than a soft sleeve. Whatever format the music is sent should be accompanied with supporting documentation. This should be brief but should include information about the song and artist, and why it is being sent. The songs should be radio-friendly (no swearing) and there should be a song list in the documentation, as well as a description of the type of music.