I always thought online subscribers were expected to complete and submit the Times Jumbos online only.
There is a list of addresses for postal submission, but due to the recent subscription debacle, I can't access that part of the site to see if there is a postal address for the Jumbos.
I complete the TLS crossword on the site and as there is no online submission available, I post it.
The only sure fire way to find out would be to email customer services on [email protected]