When email providers find out that AI are spamming the ever living shit out of things, they'll need to have a way to filter stuff. So maybe they run a fedimint or cashu mint and require a little ecash on every email to get through the filter. Same thing with ads, you want to serve me an add, attach some ecash sats and then I'll look at you're beautifully crafted 15 second video telling how great your cat backpack is.