Sorry, it's not. Modern spam filtering requires a lot of training data. Most spam that I would get - would easily bypass any small scale spam filtering operation.
My SpamAssasin 10 years ago would flag too many legitimate emails... while allowing genuine spam. The amount of crap I would get to my personal email was so bad, that I just switched to GMail for the simplicity.
It's just not worth the effort. Like it's just not worth the effort in investing into a decentralized social network at this point.
Maybe if the spam filtering protocols were public, trainable on all of the data(which isn't going to happen on a privacy focused network, ever), objectively efficient at catching spam... and runnable on even RaspberryPi 3 - you're just going to get spammed out of existence.