Google Workspace and Microsoft 365 rent mail, files, identity and meetings as one bill. Proton Mail is not the owned answer: it is another company's host. mailcow is GPL-3.0 and is a mail system you can run. That is a narrower thing than the suite people think they are replacing.
What does running mail actually mean?
Authentication, reputation, backups, and a human who answers when a customer says the invoice went to spam. A cold server does not inherit Gmail's reputation. Budget the warmup, or keep the sender and own everything else.
When is self-hosted mail the wrong project?
When nobody on the team has run mail, and the business depends on delivery tomorrow. That caveat applies here more than in any other category on this map; when should you not self-host is the long version.
What can still be owned if mail stays rented?
The archive, the routing rules, and the automation that files a message into the system of record. The inbox can stay at Google. The process that starts from the inbox does not have to.
What do we hand over?
We select the system, deploy it on infrastructure you control, connect it to the tools you keep, and write the runbook so your own team can operate it. Support after handover is optional. The rest of the map is in software you can stop renting; the engagement behind it is open-source business systems.
Name one process that still needs a person. We will tell you what a one-time build takes.
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