The following is applicable to Postfix version 2.0 and later. Earlier versions do not have support for: virtual_transport, relay_transport, virtual_alias_domains, virtual_mailbox_domains or proxy_interfaces.
local_transport (local:$myhostname)
The default mail delivery transport and next-hop destination for final delivery to domains listed with mydestination, and for [ipaddress] destinations that match $inet_interfaces or $proxy_interfaces.
virtual_transport (virtual)
The default mail delivery transport and next-hop destination for final delivery to domains listed with $virtual_mailbox_domains.
relay_transport (relay)
The default mail delivery transport and next-hop destination for remote delivery to domains listed with $relay_domains.
default_transport (smtp)
The default mail delivery transport and next-hop destination for destinations that do not match $mydestination, $inet_interfaces, $proxy_interfaces, $virtual_alias_domains, $virtual_mailbox_domains, or $relay_domains.
parent_domain_matches_subdomains (see 'postconf -d' output)
What Postfix features match subdomains of "domain.tld" automatically, instead of requiring an explicit ".domain.tld" pattern.
relayhost (empty)
The next-hop destination of non-local mail; overrides non-local domains in recipient addresses.
transport_maps (empty)
Optional lookup tables with mappings from recipient address to (message delivery transport, next-hop destination).
Available in Postfix version 2.3 and later:
sender_dependent_relayhost_maps (empty)
A sender-dependent override for the global relayhost parameter setting.
Available in Postfix version 2.5 and later:
empty_address_relayhost_maps_lookup_key (<>)
The sender_dependent_relayhost_maps search string that will be used instead of the null sender address.
Available in Postfix version 2.7 and later:
empty_address_default_transport_maps_lookup_key (<>)
The sender_dependent_default_transport_maps search string that will be used instead of the null sender address.
sender_dependent_default_transport_maps (empty)
A sender-dependent override for the global default_transport parameter setting.