License for the tzdata information

For all the years I have never worried about this, but today I got an email in my mailbox asking me "Since this is vendor imported data, we would like to register under which license this data is distributed.". Unfortunately I got not much info from Wikipedia, the tzdata or the tzcode files. The tzcode says "This code is in the public domain", but the tzdata doesn't have it, just a "This information is by no means authoritative". So... is there a license under which the tzdata is distributed? Edwin