[radialbrain]

There's also dl, which supports creating single use links for third parties to upload files: https://www.thregr.org/~wavexx/software/dl/

[nexxer]

I've been hosting dl at work for many years and it's filled our needs admirably. Simple, zero maintenance, just works.

It even has a useful Thunderbird extension that auto-uploads any large attachment using the FileLink API when composing a new mail, adding the dl URL in the email's body. Unfortunately the extension stopped working after the migration to WebExtensions.