This.
We each have an account. Login to the web interface. Choose the desired book. Click send. The epub is emailed to our Kindle.
Running calibre-web off a docker instance. Library is on my NAS.
I use the Window client to add books, handle conversions, and manage things since I have specialized plugins. You can read via the web app as well, but I prefer my ancient Paperwhite.
I vaguely remember what you’re referring to and being pretty frustrated about it. I can’t remember exactly what changed regarding clicking an emailed link. I simply don’t experience that any longer. Either Amazon stopped or I changed some setting somewhere that I’m not recalling off hand… 😬
Currently, I have calibre-web (and the windows client) set to use my email’s SMTP credentials. I then set the “sender” to an Amazon approved email. In my case, the email isn’t actually real. I just use a forwarder.
Make sure you add that sender email to the Amazon personal document approved email list.
The most recent bump I’ve had with Amazon is that they no longer accept mobi files. It’s no big deal though since they accept epubs without an issue.