Jeff Kaufman, writing about Mastodon:

Overall I’m pretty pessimistic about Mastodon, even if we only imagine futures in which lots of people move to it, because of spam. Handling spam on a centralized platform is hard but manageable; federation changes this dramatically for the worse. Imagine you’re running a server, and you get an incoming message (comment, like, DM, etc) from an account on another server. Today the default is to let it through, but as Mastodon gets larger there will be more and more money to be made in spamming there, and the larger a fraction of those incoming messages would be spam. Many of the signals centralized platforms use to detect spammers (local activity, account age, IP addresses, etc) are not available in a federated context, leaving server admins (and the software they delegate to) very little information for identifying and blocking spam. It’s at least as hard a problem as email spam filtering, probably harder because of shorter messages, and I expect this makes it very hard to run a server that doesn’t drown its users in incoming spam and reliably gets its messages out to other servers. Maybe we get to the equivalent of everyone using Gmail/Hotmail/Yahoo and anyone with a different provider has a very frustrating time?

I think that’s a reasonable concern. As he says, it’s why pretty much no one except tech weirdos runs their own mailservers anymore.

It all seems fine right now while it’s new and everyone is finding their way around and having fun. If growth on the platform continues at its current rate, though, the spammers will eventually show up. They always do.