[dnzm]

For a static site, you could use a stand-alone server like webmentiond[1]. Seems like that'd integrate similarly to what you're running now, but under your own control. There's also webmention.io[2] if you really don't want to self-host.

As for spam, the flow involves the receiver checking the sender to see if there's actually a link, before the mention is accepted. I think that is more effort than the average spammer is going to put in, although it's not 100%. Then again, neither are comments on somebody else's site.

[1]: https://webmentiond.org/ [2]: https://webmention.io/