EHLO/HELO require a domain or address-literal argument. Previously
the server accepted bare EHLO with no argument and responded 250,
which deviates from the spec and makes the honeypot easier to
fingerprint.
Two bugs fixed:
- data_received only split on CRLF, so clients sending bare LF (telnet, nc,
some libraries) got no responses at all. Now splits on LF and strips
trailing CR, matching real Postfix behavior.
- AUTH PLAIN without inline credentials set state to "await_plain" but no
handler existed for that state, causing the next line to be dispatched as
a normal command. Added the missing state handler.
