What Privnote does, in its own words
Privnote's homepage says it sends notes that will self-destruct after being read: write the note, encrypt it and get a link, send the link, and the note self-destructs when the recipient reads it. Its options let you set the note to self-destruct after reading or after one hour, 24 hours, seven days or 30 days, add a manual password, and receive an email when the note is destroyed. The page states that the note is encrypted in your browser and then stored in Privnote. It needs no account.
That is a sound design for a personal note, and sites like Privnote exist because the idea works. The limits are everything around the note: there is no dashboard to see or revoke the notes you have sent, no file attachments, and no team or audit features.