Gmail email acknowledgement | Gnotify’s 2min tutorial Show Description Gnotify is a lightweight Firefox extension that provides email acknowledgement for Gmail..

This feature is only available if you use Gmail for work or school set up by an administrator.If you use a gmail.com account, read receipts won’t work. To find out when an email you sent was opened, you can request a read receipt.

You don't have to repeat the word "acknowledge". I'd say: I'm confirming receipt of your letter of [date]. Or: This is to confirm that I have seen your email.