> I think this is one important reason that more and more emails are just links to some website with the information on it (often with a login required as well).

That's an unfortunate requirement these days.

For one, in Europe concerns around GDPR: e-mail is not guaranteed (!) to be encrypted or protected against modification in transit so it might get snooped up on its way, which makes it a no-go for sensitive stuff such as healthcare information or other highly protected classes of PII, unless PDF encryption or other ways of encryption are used... but these have the issue that UX around many of them is horrible. A link to a portal however? Easy, and provides automatically the guarantee that the other person is who they claim to be.

The second problem is deliverability: more than enough email providers still have laughably low limits (sometimes < 3MB), virus scanners don't like PDFs or ZIPs that they can't read (because they don't know the password, obviously), and on top of that come the usual anti-spam concerns.

IMHO, the best way to go would be an extra header field, think like "X-External-Attachments: https://foo.com/<uuid>.pdf <hash-alg> <hash-value>"... this could be used by MUAs to prompt the user if they wish to download and store the file, provide cryptographic checks of the file, and sidestep the issue of dumbass middleboxes yeeting password-protected files, as the files can be scanned on the endpoint side.

The second problem is deliverability: more than enough email providers still have laughably low limits (sometimes < 3MB)

What are you sending that 3MB for an email is "low"? The Bible is a little over 4MB of plain text.

I hate these EU requirements. They do nothing to help real users, and really make everything worse. Like, is it helpful that every single website now has an added banner that we have to click, but which still nobody reads and doesn't really help anything? All to avoid cookies, which are not really the source of the problem these laws were meant to address? ARRRGHHH!

As far as the file size - does that critically important message need to be embedded in a 10MB PDF? Maybe we should go back to 50k limits and force them to put that one-liner in plain text in the email. ARRRGHHH!

And get off my lawn! ARRRGHHH