This section presents additional configuration. You need to
combine this with basic configuration information as discussed the
first half of this document.
When your system is SECONDARY MX host for a remote site this
is all you need:
1 DNS:
2 the.backed-up.domain.tld IN MX 100 your.machine.tld.
3
4 /etc/postfix/
main.cf:
5
relay_domains = . . . the.backed-up.domain.tld
6
smtpd_recipient_restrictions =
7
permit_mynetworks
reject_unauth_destination
8
9 # You must specify your NAT/proxy external address.
10 #
proxy_interfaces = 1.2.3.4
11
12
relay_recipient_maps = hash:/etc/postfix/relay_recipients
13
14 /etc/postfix/relay_recipients:
15 [email protected] x
16 [email protected] x
17 . . .
When your system is PRIMARY MX host for a remote site you
need the above, plus:
18 /etc/postfix/
main.cf:
19
transport_maps = hash:/etc/postfix/transport
20
21 /etc/postfix/transport:
22 the.backed-up.domain.tld relay:[their.mail.host.tld]
Important notes:
Do not list the.backed-up.domain.tld in
mydestination.
Do not list the.backed-up.domain.tld in
virtual_alias_domains.
Do not list the.backed-up.domain.tld in
virtual_mailbox_domains.
-
Lines 1-7: Forward mail from the Internet for
"the.backed-up.domain.tld" to the primary MX host for that domain.
-
Line 10: This is a must if Postfix receives mail via a
NAT relay or proxy that presents a different IP address to the
world than the local machine.
-
Lines 12-16: Define the list of valid addresses in the
"the.backed-up.domain.tld" domain. This prevents your mail queue
from filling up with undeliverable MAILER-DAEMON messages. If you
can't maintain a list of valid recipients then you must specify
"
relay_recipient_maps =" (that is, an empty value), or you must
specify an "@the.backed-up.domain.tld x" wild-card in the
relay_recipients table.
-
Line 22: The [] forces Postfix to do no MX lookup.
Specify dbm instead of hash if your system uses
dbm files instead of db files. To find out what lookup
tables Postfix supports, use the command "postconf -m".
Execute the command "postmap /etc/postfix/transport"
whenever you change the transport table.
NOTE for Postfix < 2.2: Do not use the
fallback_relay feature
when relaying mail
for a backup or primary MX domain. Mail would loop between the
Postfix MX host and the
fallback_relay host when the final destination
is unavailable.
- In
main.cf specify "
relay_transport = relay",
- In
master.cf specify "-o
fallback_relay =" at the
end of the relay entry.
- In transport maps, specify "relay:nexthop..."
as the right-hand side for backup or primary MX domain entries.
These are default settings in Postfix version 2.2 and later.
