What do you mean with 'mail server'? Postfix? Dovecot?

Running a Postfix on anything else than a dedicated server with a static IP is a pretty bad idea (half the internet will reject the emails you send).

And to do all that just to transfer some files is probably like using an iPhone as a fly swatter.

I don't know why there's so many downvotes and patronising "fly swatter" remarks. There is a use case for this.

For example, sharing a photo album with many pictures. Or a mixtape. Or some song lyrics. I can't upload those to the cloud for copyright reasons.

Or if I want to make the transfer while away from Internet e.g. skiing, hiking, waterfall trip, etc. - there's no access to Internet services, so iCloud/Dropbox/Google Drive just won't do.

I can use lighttpd to serve the folder, but then the user has to hold down and "Save to Camera Roll" for each picture separately.

If both phones have Airdrop, then that's fine. But many phones are not iPhones. We could both install a special app for Bluetooth transfers, but we don't have Internet access, remember? So no app store.

There's a Mail client on every phone, however locked-down it is. If I can serve a collection of files over a local network and send those directly, not one at a time, then that would be very useful to me.

I think a mail server is one solution. If you can propose another flyswatter that meets my requirements, go ahead. Otherwise I still want to find a way to code a mail server, and the parent article is helpful for that.

> We could both install a special app for Bluetooth transfers, but we don't have Internet access, remember? So no app store.

Why not install the special Bluetooth app whenever you were planning to install the smtp server?

Have you considered using Nextcloud?