> more and more emails are just links to some website with the information on it (often with a login required as well)

And a 2FA SMS sent to your phone.

> If you email me a text or PDF invoice, I can always come back to it for my own reference. If you send me a link to one, there's no guarantee I can still access it later.

Download it. It sucks having to do that and maintaining your own archive instead of trusting your mailbox, but I guess there's some advantages to that as well.

Sure, I can download it if they send it as an attachment. Not so easy when it's an external reference. I guess I could login to the website and download... the web page? Well anyway I'm not going to.