$ man cheapest-route

Cheapest Route Rationale

The principle of using the most cost-effective inbox provider setup that still delivers results. Google Workspace costs more per mailbox than Microsoft 365. But cost alone doesn't determine the split — deliverability and ICP match do.

Teams overspend on email infrastructure because they don't think about cost per mailbox at scale. If you need 36 mailboxes and Google Workspace costs $7/user/month while Microsoft 365 costs $6/user/month, that's a $36/month difference. Not huge — but it adds up across multiple partner campaigns. The cheapest route isn't always the best route. It's the one that balances cost with deliverability for your specific ICP.

I factor cost into the provider split but I don't optimize purely for price. If a partner's ICP is 80% Google, I'm not going to use Microsoft mailboxes because they're cheaper. I go Google because that's where deliverability is highest. But for the 20% that's Microsoft, I use Microsoft 365 at its lower price point. The cheapest route is the one that doesn't waste money sending to the wrong provider.