FileInfo.com - The File Extensions Resource

.POSTAL File Extension

File Type	TomTom Postal Code File
File Format	File
Common?	No
File Description	Data file referenced by TomTom GPS navigation software; maps zip codes (or postal codes) to cities, streets, and other locations; accessed by TomTom software and should not be opened manually.
Program(s) that open postal files	Mac / Windows: TomTom HOME Pocket PC: TomTom Navigator

Information from FileInfo.com - The File Extensions Resource.
http://www.fileinfo.com/extension/postal