The notifications you can set up to a normal email address invariably only say that institution X sent you a message, but never specify the topic. That means you have to login to see if it is actually important and actionable or just something you already knew or a confirmation of something you submitted.
Even worse is this common scenario:
* Get notification that X sent something to Berichtenbox
* Login to Berichtenbox (first get mobile phone for required 2FA)
* Message says new information is available in X's web portal
* Login to X's web portal (mijn.somethingsomething.nl)
* Read totally pointless message that could even have been sent in plain email
Compare this to the postal flow:
* Get letter, read it
I think these days you can deactivate Berichtenbox and receive important information via post again, but this was not an option in the first year or so, so even experimenting with it was risky.
* email notifications are unreliable * messages are considered delivered a week after landing in your data box, regardless of you reading them * old messages are automatically deleted after 90 days (!!!) unless you pay for an expensive and cumbersome archive addon service
Especially point number three makes the whole thing quite dangerous, not just liability - you might get an important message/request from the state while on long vacation/loose the notification and it will self erase - mission impossible style! And you will only find out when you re in trouble for not doing something important later...
Unless you plan to work with the data box daily and manually check the messages its really dangerous to use it.
1. You can an email in your regular email stating that there is a new message in your Berichteninbox. (No clickable link, presumably to avoid phishing.)
2. You go to mijn.overheid.nl to access your Berichteninbox. You sign in with DigID.
3. You open the mentioned message, which says a PDF with the actual letter is attached.
4. You open the PDF.
5. The PDF says you'll be able to file your tax returns a month from now.
BTW, if said PDF contains an iDeal payment link, you can switch to yet another app (your banking app) and back (probably via website in between) and immediately pay things. Which is nice, but again watching over the shoulder of someone going through these actions it may seem that the phone is going crazy switching between apps :)
Btw, a nice insight into email is also that it is one of the very few systems that decouples protocol from provider (Matrix and xmpp do that too, not widely adopted sadly) AND also has critical adoption (which Whatsapp also has in my country, sadly we are stuck with Meta there). We should never give up email because we will likely never get an open and free system like that back without some kind of government intervention. (Even though we all know email is a sub-optimal pile of hacks.)