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I have just seen https://www.helpnetsecurity.com/2023/03/28/exchange-online-blocking-emails-from-vulnerable-servers/ and thought I'd bring it to peoples attention in case if affects anyone here.
This is only going to be a good thing. So many organisations have dragged their feet on upgrading on-prem exchange servers.
Sure, you can bitch and moan about MSFT blocking whatever, but honestly if you're running Exchange 2007 still, you deserve what you get.