The discussion around how to prove you sent a letter, or someone received it, has already been discussed to death on the internet. But I can't find anything for the other way round; how to prove someone else sent you physical mail.
Hypothetical scenario: A Tenant wishes to serve notices to a landlord but the landlord has not provided an address in England an Wales as specified by section 48. The landlord provides the tenant with a fake address. The tenant then starts proceedings against the landlord to this fake address, and wins a court case by default. The landlord then claims the address that was sent in the letter, isn't his address, and that the tenant fabricated it. Can the tenant do anything to prove the landlord did in fact send that letter?