> they've already failed to meet me halfway in communication

This hypothetical doesn’t seem to make sense (maybe I’m missing something). If the person is communicating ineffectively in email, what does it solve to send them a Slack (or whatever) message that simply reads, “hi”?

What a weird take. Unless you have immaculate email filtering or receive very few emails, it’s not hard for emails to slip through the cracks. You can complain about someone “not meeting half way” in a phone call or IM with read receipts, but email is one way communication until you actually get a response.