Ask HN: Why is an email I deleted from gmail 3 years ago still on their servers?

As mentioned I deleted an email from my gmail account and trash 3 years ago, but kept a direct link to the original before doing so and have been monitoring it. It's been 3 years and that direct link still works. The email is nowhere to be found in my gmail account. This strikes me as odd and could possibly be used as a covert communication channel that would never get detected. Example send a bunch of emails between 2 accounts. Keep all the direct links to the emails. Delete all emails in both accounts. If anyone were to log into either account they would see nothing unless you had the direct links to the individual emails. Thoughts?