[skissane]

Big e-mail providers are primarily concerned with spam–which is defined by the volume and unsolicited nature of the messages, rather than the opinions they express. Sometimes their attempts at stopping it impose collateral damage, and their response to that collateral damage can be arbitrary and capricious–but that's a different issue from what we are talking about with Mastodon coordinated de-federation, which is much more intentional than collateral.

The terms of service of those big providers say that they can ban people for "hate speech", but in practice they rarely do that, and on the rather rare occasions they do, it is usually a particularly egregious case of it.

By contrast, the big Mastodon instances seem to be very keen on banning "hate speech" – and defining that term in a much broader way than most other platforms do. See https://joinmastodon.org/covenant point 1