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Mail being deferred with unknown mail transport error

From: Rich Bishop <rjb38_at_nospam>
Date: Fri Oct 01 2010 - 16:29:16 GMT
To: postfix-users@postfix.org

I have a RHEL5 machine running Redhat's build of postfix 2.3.3 and am having
problems with messages being sporadically deferred with 'unknown mail transport
error'.

The machine is a gateway for listserv, so it does receive lots of mail at
times. It appears that the problem is related to the amount of mail being queued
- if I do a postqueue -f, most of the problem messages are again deferred with
the same error. If I slowly put the back onto the queue with postsuper -r <qid>
; sleep 1 then most messages flow through without any problems.

I've done some debugging - postfix appears to be successfully looking up the
user in LDAP and getting a mailhost, but fails before it opens an smtp
connection to the mailhost.

Here's some verbose output from qmgr:

Sep 30 20:22:18 jay postfix/qmgr[10510]: send attr address = <user1>@DREXEL.EDU
Sep 30 20:22:18 jay postfix/qmgr[10510]: private/rewrite socket: wanted attribute: flags
Sep 30 20:22:18 jay postfix/qmgr[10510]: input attribute name: flags
Sep 30 20:22:18 jay postfix/qmgr[10510]: input attribute value: 0
Sep 30 20:22:18 jay postfix/qmgr[10510]: private/rewrite socket: wanted attribute: transport
Sep 30 20:22:18 jay postfix/qmgr[10510]: input attribute name: transport
Sep 30 20:22:18 jay postfix/qmgr[10510]: input attribute value: smtp
Sep 30 20:22:18 jay postfix/qmgr[10510]: private/rewrite socket: wanted attribute: nexthop
Sep 30 20:22:18 jay postfix/qmgr[10510]: input attribute name: nexthop
Sep 30 20:22:18 jay postfix/qmgr[10510]: input attribute value: [<mailhost>.irt.drexel.edu]
Sep 30 20:22:18 jay postfix/qmgr[10510]: private/rewrite socket: wanted attribute: recipient
Sep 30 20:22:18 jay postfix/qmgr[10510]: input attribute name: recipient
Sep 30 20:22:18 jay postfix/qmgr[10510]: input attribute value: <user1>@DREXEL.EDU
Sep 30 20:22:18 jay postfix/qmgr[10510]: private/rewrite socket: wanted attribute: flags
Sep 30 20:22:18 jay postfix/qmgr[10510]: input attribute name: flags
Sep 30 20:22:18 jay postfix/qmgr[10510]: input attribute value: 4096
Sep 30 20:22:18 jay postfix/qmgr[10510]: private/rewrite socket: wanted attribute: (list terminator)
Sep 30 20:22:18 jay postfix/qmgr[10510]: input attribute name: (end)
Sep 30 20:22:18 jay postfix/qmgr[10510]: resolve_clnt: `owner-drexel-official-students-all-l@LISTS.DREXEL.EDU' -> `<user1>@DREXEL.EDU' -> transp=`smtp' host=`[<mailhost>.irt.drexel.edu]' rcpt=`<user1>@DREXEL.EDU' flags= class=default
Sep 30 20:22:18 jay postfix/qmgr[10510]: start sorted recipient list
Sep 30 20:22:18 jay postfix/qmgr[10510]: qmgr_message_sort: <user1>@DREXEL.EDU
Sep 30 20:22:18 jay postfix/qmgr[10510]: qmgr_message_sort: <user2>@DREXEL.EDU
Sep 30 20:22:18 jay postfix/qmgr[10510]: end sorted recipient list
Sep 30 20:22:18 jay postfix/qmgr[10510]: private/smtp socket: wanted attribute: status
Sep 30 20:22:18 jay postfix/qmgr[10510]: warning: premature end-of-input on private/smtp socket while reading input attribute
 name
Sep 30 20:22:18 jay postfix/qmgr[10510]: warning: private/smtp socket: malformed response
Sep 30 20:22:18 jay postfix/qmgr[10510]: qmgr_transport_throttle: transport smtp: status: 4.3.0 reason: unknown mail transport error
Sep 30 20:22:18 jay postfix/qmgr[10510]: warning: transport smtp failure -- see a previous warning/fatal/panic logfile record for the problem description

The output from postconf -n:

alias_database = hash:/etc/aliases
alias_maps = hash:/etc/aliases
bounce_queue_lifetime = 3d
command_directory = /usr/sbin
config_directory = /etc/postfix
daemon_directory = /usr/libexec/postfix
debug_peer_level = 2
fast_flush_domains = drexel.edu, cabrini.edu, medaille.edu
html_directory = no
in_flow_delay = 0
inet_interfaces = all
local_recipient_maps = $alias_maps
mail_owner = postfix
mailq_path = /usr/bin/mailq.postfix
manpage_directory = /usr/share/man
maximal_queue_lifetime = 3d
mydestination = localhost
myhostname = lists.drexel.edu
mynetworks = 127.0.0.0/8
newaliases_path = /usr/bin/newaliases.postfix
queue_directory = /var/spool/postfix
readme_directory = /usr/share/doc/postfix-2.3.3/README_FILES
relay_domains = $mynetworks, $mydestination, lists.irttest.drexel.edu, lists.drexel.edu
relay_recipient_maps = hash:/etc/postfix/aliases, ldap:ldappresence-lists, ldap:ldappresence-drexeltestlists
sample_directory = /usr/share/doc/postfix-2.3.3/samples
sendmail_path = /usr/sbin/sendmail.postfix
setgid_group = postdrop
smtpd_client_restrictions = cidr:/etc/postfix/client_access
transport_maps = hash:/etc/postfix/transport, ldap:ldaproute-drexel, ldap:ldaproute-cabrini, ldap:ldaproute-drexel.com
unknown_local_recipient_reject_code = 550

Please let me know if there's any more output that would be useful in debugging
this.

Thanks,

Rich