And today I see an announcement from a large German mailbox provider offering a similar service for residents of the Federal Republic of Germany. Deutsche Post is working with 1&1 (GMX and Web.de) to start this new letter announcements service.
From the announcement (translated): "Registered users can conveniently be informed in advance by email about incoming mail. A photo of the envelope is attached to the notification email. This means that users are always informed about which mail they are receiving on the web and in the smartphone apps from WEB.DE and GMX. The service is free of charge and can be activated by all 34 million GMX and WEB.DE users from July 27, 2020 directly in the settings of their own email account."
Users simply register their postal address, then Deutsche Post validates that registration by snail mailing a confirmation code (how's that for a double opt-in?) and after the registration and validation are complete, notifications about what's coming to their mailbox will be emailed directly to them. Pretty neat!