Configuration and reflection

[novedevo]

Sail needs to know what its hostname is in order to properly validate paths (environment variable? toml config?), and needs a list of hostnames that it knows how to forward to to support 251 and 551 commands. The second of those isn't necessary since we can just return errors for anything not on the same host, though.

[novedevo]

we should also include our hostname in our initial connection readiness statement and other related places. Anywhere we currently say Sail.

[gennyble]

I'd like to be able to accept mail for more than one domain. OpenSMTPD seems to handle the "which domain do I present" issue, when handling multiple domains, by leaving it entirely up to the host to configure.

To set the hostname that smtpd presents itself as over smtp, you put the name in /etc/smtpd/mailname, otherwise it seems to check your /etc/hosts for what maps to 127.0.1.1.