Further, given how poorly humor — especially sarcastic or snarky, even if mild — translates in text, you're running a moderate risk of pissing someone off through no fault of their own, for no reason other than to indulge yourself.
If instead you ask your co-workers to cc or bcc on replies then you will know which have been dealt with. (I think for internal mails it’s more reasonable to ask that if the original person contacts someone else, they cc you so you know who is dealing – and in smaller organisations where people know you personally you could also send a mail round the day before you leave to say you’re going to be out and to ask that any enquiries are directed to [name]in your absence, to try to avoid them coming into your inbox in the first place.

John Whatsisname has retired. Please contact [insert name and email] for enquiries relating to [subjects], or myself at [email] for personal matters. Thank you to my colleagues and clients for your support over the years.
You’ve worked to make your email clear, and you’ve carefully edited to streamline your writing.The body of your email might well be perfect, but it can all go awry if you use the wrong sign-off. It’s just a word or a short phrase, followed by your signature, and yet finding the right tone to close your email often requires a surprising amount of thought and finesse.