Why smtp instead of relay?

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Why smtp instead of relay?
\ Etienne Pretorius (16 May 2007)
. \ Victor Duchovni (16 May 2007)
. \ Noel Jones (16 May 2007)

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Subject:	Why smtp instead of relay?
Group:	Postfix-users
From:	Etienne Pretorius
Date:	16 May 2007

Hello list,

I need some clarification, you see I am trying to configure a machine to
relay domains I host to the pop server via the relay daemon while still
being able to smtp out any emails I receive from $mynetworks.

As far as I understand it, postfix should accept emails that match
$relay_domains and it does but the document
(http://www.postfix.org/postconf.5.html#relay_domains) continues and
says that:

"Domains that match $relay_domains are delivered with the
$relay_transport mail delivery transport. The SMTP server validates
recipient addresses with $relay_recipient_maps and rejects non-existent
recipients. See also the relay domains address class in the
ADDRESS_CLASS_README file."

Well I took a look and on my system the $relay_transport = relay. So I
thought that since relay is a copy of smtp that I'll just add the
relayhost directive to the pop server and that should solve my problem.

master.cf:
# When relaying mail as backup MX, disable fallback_relay to avoid MX loops
relay unix - - - - - smtp
-o relayhost=[ip.add.re.ss]
-o fallback_relay=

But I still see the incoming email being routed out via smtp instead of
relay regardless of what network I am comming from ie (mynetwork client
or not). I would have expected that mynetwork clients would default to
smtp while relay_domains would default to relay....

mail.log dump:

May 16 14:41:12 postfix/smtpd[25320]: connect from SOMEHOST[SOMEIP]
May 16 14:41:28 postfix/smtpd[25320]: NOQUEUE: client=SOMEHOST[SOMEIP]
May 16 14:41:40 amavis[6956]: (06956-02) ESMTP::10024
/var/lib/amavis/amavis-20070516T135104-06956: <sender-address> ->
<receiving-address>
Received: from localhost ([127.0.0.1]) by localhost (localhost
[127.0.0.1]) (amavisd-new, port 10024) with ESMTP for
<receiving-address>; Wed, 16 May 2007 14:41:28 +0000 (UTC)
May 16 14:41:46 amavis[6956]: (06956-02) Checking: 0uuE-qqt-T8y [SOMEIP]
<sender-address> -> <receiving-address>
May 16 14:41:46 amavis[6956]: (06956-02) cached
f39d6f12ad323d9da5abc2ac100ff4a2 from <sender-address> (0,0)
May 16 14:41:46 amavis[6956]: (06956-02) p001 1 Content-Type:
text/plain, size: 14 B, name:
May 16 14:41:46 postfix/smtpd[25437]: connect from localhost[127.0.0.1]
May 16 14:41:46 postfix/smtpd[25437]: 4D1EEACB68:
client=localhost[127.0.0.1]
May 16 14:41:46 postfix/cleanup[25438]: 4D1EEACB68:
message-id=<20070516144146.4D1EEACB68@localhost>
May 16 14:41:46 postfix/smtpd[25437]: disconnect from localhost[127.0.0.1]
May 16 14:41:46 postfix/qmgr[25291]: 4D1EEACB68: from=<sender-address>,
size=830, nrcpt=1 (queue active)
May 16 14:41:46 amavis[6956]: (06956-02) FWD via SMTP: <sender-address>
-> <receiving-address>, 250 2.6.0 Ok, id=06956-02, from
MTA([127.0.0.1]:10025): 250 2.0.0 Ok: queued as 4D1EEACB68
May 16 14:41:46 amavis[6956]: (06956-02) Passed CLEAN, [SOMEIP] [SOMEIP]
<sender-address> -> <receiving-address>, mail_id:
0uuE-qqt-T8y, Hits: -, queued_as: 4D1EEACB68, 17923 ms
May 16 14:41:46 amavis[6956]: (06956-02) TIMING [total 17928 ms] - SMTP
EHLO: 28 (0%)0, SMTP pre-MAIL: 6 (0%)0, SMTP pre-DATA-flush: 11516
(64%)64, SMT
P DATA: 6188 (35%)99, body_digest: 1 (0%)99, gen_mail_id: 0 (0%)99,
mime_decode: 7 (0%)99, get-file-type1: 15 (0%)99, decompose_part: 1
(0%)99, parts_decode:
0 (0%)99, update_cache: 3 (0%)99, decide_mail_destiny: 0 (0%)99,
fwd-connect: 33 (0%)99, fwd-mail-from: 2 (0%)99, fwd-rcpt-to: 24 (0%)99,
fwd-data-cmd: 1 (0%)
99, write-header: 1 (0%)99, fwd-data-contents: 1 (0%)99, fwd-data-end:
86 (0%)100, fwd-rundown: 2 (0%)100, prepare-dsn: 1 (0%)100,
main_log_entry: 10 (0%)100,
update_snmp: 1 (0%)100, unlink-1-files: 1 (0%)100, rundown: 0 (0%)100
May 16 14:41:46 postfix/smtp[25439]: warning: host
SENDERMX[SENDERMXIP]:25 greeted me with my own hostname
May 16 14:41:46 postfix/smtp[25439]: warning: host
SENDERMX[SENDERMXIP]:25 replied to HELO/EHLO with my own hostname
May 16 14:41:46 postfix/smtp[25439]: 4D1EEACB68:
to=<mapped-receiving-address>, orig_to=<receiving-address>,
relay=SENDERMX[SENDERMXIP]:25, delay=0.18, delays=0.11/0.04/0.02/0,
dsn=5.4.6, status=bounced (mail for SENDER-DOMAIN loops back to myself)
May 16 14:41:46 postfix/cleanup[25438]: 7966CACB71:
message-id=<20070516144146.7966CACB71@localhost>
May 16 14:41:46 postfix/bounce[25440]: 4D1EEACB68: sender non-delivery
notification: 7966CACB71
May 16 14:41:46 postfix/qmgr[25291]: 7966CACB71: from=<>, size=2725,
nrcpt=1 (queue active)
May 16 14:41:46 postfix/qmgr[25291]: 4D1EEACB68: removed
May 16 14:41:46 postfix/smtp[25439]: warning: host
SENDERMX[SENDERMXIP]:25 greeted me with my own hostname
May 16 14:41:46 postfix/smtp[25439]: warning: host
SENDERMX[SENDERMXIP]:25 replied to HELO/EHLO with my own hostname
May 16 14:41:46 postfix/smtp[25439]: 7966CACB71: to=<sender-address>,
relay=SENDERMX[SENDERMXIP]:25, delay=0.03, delays=0.01/0/0.01/0,
dsn=5.4.6, status=bounced (mail for SENDER-DOMAIN loops back to myself)
May 16 14:41:46 postfix/qmgr[25291]: 7966CACB71: removed
May 16 14:41:53 postfix/smtpd[25320]: disconnect from SOMEHOST[SOMEIP]