I have just sent my first roll of film to a film processor that develops your film, sends your prints, and puts scans online (and will print you digital photos as well, plus other services). But I know you’re not supposed to freeze film. What problems could I expect when I drop my mailing envelope in an outdoor mailbox to be stored on an unheated cargo compartment in a truck when the temperatures get well below freezing?
There is nothing wrong with freezing film. Some photographers routinely freeze large amounts of film so that they can puchase in bulk from the same batch, thus ensuring consistency over several years. You do have to be careful that the film is thawed when both used and processed, and also that it remains in it’s container whilst it warms up to avoid condensation forming. Your film will probably be OK as the mail room of the lab will not be so cold and will allow your film to reach an OK temp quite slowly.