Hi squiddo
Welcome to the Community Forums.
There are a lot of restrictions when it comes to transferring emails from one account to another. From your description, the emails in your older account are what we would call orphaned and should have been deleted within the 90 days after your disconnection, which coenoby has kindly advised. Our email service is only available to customers with active broadband accounts, so the use of the emails has been available to you when you should not have been entitled to the service. Sometimes emails are removed when the system is 'swept' of any orphaned accounts, and there are sometimes when emails are missed out.
Emails are stored within the online account services, and it is the transfer of the online account services to another account which would includes any linked emails. As it has been 36 months as you say, since the account disconnected, the online account services may be inaccessible. Meaning we wouldn't be able to transfer this over. It's also important to understand that when transferring the online account and emails to another account, that both accounts are under the same account holder name, we are unable to transfer online accounts and email services to two accounts under different account holders.
If these emails are older emails, such as ntlword, blueyonder or virgin.net emails, I would highly recommend you save any important emails as soon as possible as there are always random 'sweeps', to remove orphaned accounts.
Let us know if you've any further questions on what we've advised above.