We have strict rules for our customer service people not to respond to what seems to be a bot, since all the "agent" based communication we get is for conducting scams. It is never worthwhile to engage with or pursue.
If we lose a sale or two, that's okay.
The more interesting shift isnt whether humans will keep using email with agents, but whether agents can become distinguishable from noise. Historically, we ignored anonymous calls but we engaged with known vendors that had reputation, contracts, and consequences.
Once an agent has a persistent identity/a domain, trust becomes something that can be accumulated over time instead of being assumed per message.