For now, this is all [documented in a separate server-setup document](https://github.com/tildeclub/tilde.club/blob/master/docs/server.org); ultimately, I presume we'll consolidate it all here.
The default MTA on CentOS is `postfix`. Our goal was to have a `localhost`-only mail service, which required that we configure `postfix` to listen only to `localhost`, and to bounce any email which local users try to send off-server. Both configuration changes are handled in `/etc/postfix/main.cf`.
* the `default_transport` parameter should be the bounce message we want (so add `default_transport = error: outside mail is not deliverable` to the bottom of the file)
Users will connect from their shell account to an IRC server, so it is *very* handy to have an `identd` server. For us that just meant installing the standard CentOS `identd` server and configuring it to start automatically: