I've noticed similar accounts commenting on YouTube.

They have been created years ago with minimal information, and suddenly they come out and go full throttle with pro-Russian arguments in debates on videos related to the US, EU and Ukraine.

It's not ideal that Hetzner is hosting the email for them, but then again - if the Hetzner account is created by a EU citizen with Russian ties, it's almost impossible to detect.

Personally I would contact the account owner and ask them a couple of follow-up questions and tell them to go elsewhere if I felt something was fishy.

Sounds like sleeper bot accounts.

They're most likely monitoring your public instance feed, including non-federated instance-local-only posts as I noticed some aren't following other accounts, but check if an account is following them.

I'd also check for any unexpected traffic to/from your instance on the wire when there shouldn't be any, just in case.

But it's concerning.

I think IFTAS had a post quite recently about a whole botnet that's creating tons of accounts, behaving kind of normally for awhile before they start doing... whatever it is they start doing (wow, having a short sleep is doing wonders for the memory).

It's also worthy to note, with Mastodon, users can setup interactions to be filtered under a special area in notifications for news accounts, as well as other settings... So, if a new account tries to send spam within the first 30 days, it will get filtered behind a special area in notifications. They could be for future nefarious use,