Were you using simplelogin.io, which is part of Proton? It is actually possible to reply or send mails from the aliases you create there. The feature is called reverse-alias.

I tried that, but I much prefer the haptics of real paper and writing with an actual pen. Also, I really like the look of ink on paper. Of course, there are still cases when a tablet is just the best. For example, when annotating PDFs.

pro tip: you can still write ugly if you use a fountain pen

Yes, but for my own notes it's not a problem if the handwriting is ugly. I still like to write by hand, even if my handwriting looks pretty messy.