After I followed the steps from the answer: My old SO account was registered with my previous work email I completed the form and received an email that said:
If you are unable to log into one of them, complete as much as you can with the verifications and I will see if I can verify your ownership between the accounts.
What verification is needed, I don't have access to the old email, actually the old email is no more valid, what do I know is:
- the email used to create that account and the fact that is no longer valid;
- the IPs with which I browsed SO at that time;
- the fact that I deleted the old email gravatar associated with the old account around the same time I created this SO account I'm writing now with.
Is this enough to prove my ownership of that account?