Ink on paper, where I work. There have been court decisions that have seen Fax as "remote copying". And said that those remote copies only had any legal value if there was an actual paper original. Thus the workflow always has to involve paper that is then archived as paper in a folder...

I once had to print a form and fax to a company with a signature and the instructions said specifically that "signing with a computer and sending digitally is not allowed".

I just signed with macOS Preview, applied some random noise filter and used a one-off online fax service. ¯\_(ツ)_/¯

On our end, it's all electronic - we never print anything out. So yeah, on our side, "email with extra steps". But I have no idea how the mortgage companies handle it on their end.