Unlike what we wrote in 2014 (cf. 4fb4be4d279dd94cab33fc778cfa318b93d6926f)
the postscreen(8) server can run chrooted, meaning we can also chroot
the smtpd(8), tlsproxy(8), dnsblog(8) and cleanup(8) daemons.

These addresses need to be accepted on the MX:es, as recipients
sometimes phone back during the SMTP session to check whether the sender
exists.

Since a time-dependent suffix is added to the local part (cf.
http://www.postfix.org/postconf.5.html#address_verify_sender_ttl) it's
not enough to drop incoming mails to ‘double-bounce@fripost.org’, and
it's impractical to do the same for /^double-bounce.*@fripost\.org$/.

‘noreply@’ aliases can be added by routing them to
‘@discard.fripost.org’.

In particular, since Postfix is now able to perform LDAP lookups using
SASL, previous hacks with simble binds on cn=postfix,ou=services,… can
now be removed.

It has to be performed last, to give a chance to be accepted as a
regular mailbox.

We introduce a new, dedicated, smtpd daemon whose only purpose is to
resolve catch-alls.

Instead, we pretend that lists are valid users (via a match in the
mailbox_transport_maps) but choose a different transport (with the same
request in transport_maps).

The advantage is that we get rid of the ugly hack for list transport…

A minor drawback is that we now have two LDAP lookups instead of one for
non local addresses (ie, everything but reserved addresses). Hopefully
the requests are cached; but even if they aren't, querying a local LDAP
server is supposed to be cheap.

Other abreviations are upper case.