We also have integrated project honeypot, akismet, and captcha, but those are passive technologies that can be worked around given time.
But simple is best — raise the bar of contribution just a tiny bit, and the effect on spam is huge. To get around a post queue, spammers have to make a quality contribution, and that's hard when spam accounts are automated by script.
Does #mastodon support any of this?
The silver lining to this: if you have this enabled by default and a server exists with poor or absent moderation... well, no spam gets approved 👋