Renting mailboxes from Google Workspace or Microsoft 365 runs roughly $3–7 per mailbox per month, and providers restrict cold-email use on their consumer-facing plans. Self-hosting on your own domain changes the cost base and removes per-seat limits — but it requires authentication, warmup, and abuse controls done correctly, which is the actual work, not an afterthought.
The trade is cost and control versus convenience. Workspace and Microsoft 365 are turnkey but priced per seat and governed by acceptable-use policies that discourage or prohibit cold outreach; scaling outbound means buying many seats and risking account action. Self-hosted sending — running your own mail transfer agent on infrastructure you control, sending from your own domain — changes the per-message cost base and removes per-seat ceilings. It is not free of work: you own authentication setup, a correct warmup ramp, suppression and bounce handling, and abuse controls, and you carry responsibility for reputation. That last point is the real differentiator between a cheap setup and a durable one — abuse control and reputation operations are where most self-hosted attempts fail. Humerly provides the self-hosted path as a managed control plane: you bring the domain, and the platform handles the sending stack, the pre-send audit, warmup, and monitoring — so the cost and control benefits come without rebuilding mail infrastructure from scratch. (Exact per-inbox economics are shared in a sales conversation, not published.)