Earlier quoted context omitted.
One thing I like about Fastmail is the ability to serve static web content directly from the “Files” section of their apps/website. Since they already manage the domain for email, spinning up static sites at subdomains is really easy and really nice.
I almost did this, but they don't have rsync access to the Files space. It's really nice with a static site being able to use rsync to just update the changed files.
Edit: I’m pretty sure the sync options are part of the put command