I have postfix mail server on ubuntu 18, which act as a relay email server for a couple virtual machines and as an imap/smtp server for our colleges. If I send an email from a mail client with smtp directly through the relay server, the email is signed by the server correctly.
However if I send an email from a VM, through the VM's postfix server, which forwards everything to the relay server, then the message will be not signed. Here is the appropriate part of the mail.log of the relay server:
Mar 29 15:43:15 zg-3 postfix/pickup[6925]: D6775A2CE0: uid=1002 from=<v2@v0402.zg-3.mydomain.org>
Mar 29 15:43:15 zg-3 postfix/cleanup[9282]: D6775A2CE0: message-id=<20220329134315.8342C40412@v0402.zg-3.mydomain.org>
Mar 29 15:43:15 zg-3 postfix/qmgr[28882]: D6775A2CE0: from=<v2@v0402.zg-3.mydomain.org>, size=1005, nrcpt=1 (queue active)
Mar 29 15:43:18 zg-3 postfix/smtp[9292]: D6775A2CE0: to=<nagyt@destination.org>, relay=mail.destination.org[109.61.0.141]:25, delay=2.4, delays=0.01/0.01/0.16/2.2, dsn=2.0.0, status=sent (250 2.0.0 from MTA(smtp:[127.0.0.1]:10025): 250 2.0.0 Ok: queued as 31688123853)
Mar 29 15:43:18 zg-3 postfix/qmgr[28882]: D6775A2CE0: removed
My /etc/opendkim/trusted.hosts:
127.0.0.1
localhost
*.mydomain.org
My /etc/opendkim/key.table:
default._domainkey.mydomain.org mydomain.org:default:/etc/opendkim/keys/mydomain.org/default.private
And I have the key in the correct file (note, that the directly sent email is using the
same key for signing correctly):
$ ls -l /etc/opendkim/keys/mydomain.org/default.*
-rw------- 1 opendkim opendkim 1675 Jun 25 2018 /etc/opendkim/keys/mydomain.org/default.private
-rw------- 1 root root 495 Jun 25 2018 /etc/opendkim/keys/mydomain.org/default.txt
My /etc/postfix/main.cf:
smtpd_banner = $myhostname ESMTP $mail_name (Ubuntu)
biff = no
# appending .domain is the MUA's job.
append_dot_mydomain = no
# Uncomment the next line to generate "delayed mail" warnings
#delay_warning_time = 4h
readme_directory = no
myhostname = zg-3.mydomain.org
alias_maps = hash:/etc/aliases
alias_database = hash:/etc/aliases
myorigin = mydomain.org
mydestination = zg-3.mydomain.org, localhost.mydomain.org, localhost
relayhost =
mynetworks = 127.0.0.0/8 [::ffff:127.0.0.0]/104 [::1]/128 zg-2.mydomain.org zg-3.mydomain.org lu1.mydomain.org 172.16.0.0/16
# 50 MB
message_size_limit = 52428800
### TLS parameters
smtpd_tls_cert_file=/etc/ssl/certs/ssl-cert-snakeoil.pem
smtpd_tls_key_file=/etc/ssl/private/ssl-cert-snakeoil.key
smtpd_use_tls=yes
smtpd_tls_session_cache_database = btree:${data_directory}/smtpd_scache
smtp_tls_session_cache_database = btree:${data_directory}/smtp_scache
### Dovecot SMTP authentication
smtpd_sasl_type = dovecot
smtpd_sasl_path = private/auth
smtpd_sasl_auth_enable = yes
# With Postfix version before 2.10, use smtpd_recipient_restrictions
#smtpd_relay_restrictions = permit_mynetworks, permit_sasl_authenticated, reject_unauth_destination
smtpd_recipient_restrictions = permit_mynetworks, permit_sasl_authenticated, reject_unauth_destination
# Milter configuration
# OpenDKIM
milter_default_action = accept
milter_protocol = 6
smtpd_milters = local:/opendkim/opendkim.sock
non_smtpd_milters = local:/opendkim/opendkim.sock
mailbox_size_limit = 0
virtual_mailbox_limit = 0
recipient_delimiter = +
inet_interfaces = all
### Configuration for virtual mailboxes
home_mailbox = Maildir/
virtual_mailbox_domains = /etc/postfix/vhosts
virtual_mailbox_base = /home/vmail
virtual_mailbox_maps = hash:/etc/postfix/vmaps
virtual_minimum_uid = 1000
virtual_uid_maps = static:1002
virtual_gid_maps = static:1002
virtual_transport = dovecot
spamassassin_destination_recipient_limit = 1
dovecot_destination_recipient_limit = 1
My /etc/postfix/master.cf:
# Postfix master process configuration file. For details on the format
# of the file, see the master(5) manual page (command: "man 5 master").
#
# Do not forget to execute "postfix reload" after editing this file.
#
# ==========================================================================
# service type private unpriv chroot wakeup maxproc command + args
# (yes) (yes) (yes) (never) (100)
# ==========================================================================
smtp inet n - - - - smtpd
-o content_filter=spamassassin
#smtp inet n - - - 1 postscreen
#smtpd pass - - - - - smtpd
#dnsblog unix - - - - 0 dnsblog
#tlsproxy unix - - - - 0 tlsproxy
submission inet n - - - - smtpd
-o syslog_name=postfix/submission
# SSL/TLS
-o smtpd_tls_wrappermode=yes
# STARTTLS
# -o smtpd_tls_security_level=encrypt
-o smtpd_sasl_auth_enable=yes
-o smtpd_client_restrictions=permit_sasl_authenticated,reject
-o milter_macro_daemon_name=ORIGINATING
smtps inet n - - - - smtpd
-o syslog_name=postfix/smtps
# SSL/TLS
-o smtpd_tls_wrappermode=yes
# STARTTLS
# -o smtpd_tls_security_level=encrypt
-o smtpd_sasl_auth_enable=yes
-o smtpd_client_restrictions=permit_sasl_authenticated,reject
-o milter_macro_daemon_name=ORIGINATING
#628 inet n - - - - qmqpd
pickup fifo n - - 60 1 pickup
cleanup unix n - - - 0 cleanup
qmgr fifo n - n 300 1 qmgr
#qmgr fifo n - n 300 1 oqmgr
tlsmgr unix - - - 1000? 1 tlsmgr
rewrite unix - - - - - trivial-rewrite
bounce unix - - - - 0 bounce
defer unix - - - - 0 bounce
trace unix - - - - 0 bounce
verify unix - - - - 1 verify
flush unix n - - 1000? 0 flush
proxymap unix - - n - - proxymap
proxywrite unix - - n - 1 proxymap
smtp unix - - - - - smtp
relay unix - - - - - smtp
# -o smtp_helo_timeout=5 -o smtp_connect_timeout=5
showq unix n - - - - showq
error unix - - - - - error
retry unix - - - - - error
discard unix - - - - - discard
local unix - n n - - local
virtual unix - n n - - virtual
lmtp unix - - - - - lmtp
anvil unix - - - - 1 anvil
scache unix - - - - 1 scache
#
# ====================================================================
# Interfaces to non-Postfix software. Be sure to examine the manual
# pages of the non-Postfix software to find out what options it wants.
#
# Many of the following services use the Postfix pipe(8) delivery
# agent. See the pipe(8) man page for information about ${recipient}
# and other message envelope options.
# ====================================================================
#
# maildrop. See the Postfix MAILDROP_README file for details.
# Also specify in main.cf: maildrop_destination_recipient_limit=1
#
maildrop unix - n n - - pipe
flags=DRhu user=vmail argv=/usr/bin/maildrop -d ${recipient}
#
# ====================================================================
#
# Recent Cyrus versions can use the existing "lmtp" master.cf entry.
#
# Specify in cyrus.conf:
# lmtp cmd="lmtpd -a" listen="localhost:lmtp" proto=tcp4
#
# Specify in main.cf one or more of the following:
# mailbox_transport = lmtp:inet:localhost
# virtual_transport = lmtp:inet:localhost
#
# ====================================================================
#
# Cyrus 2.1.5 (Amos Gouaux)
# Also specify in main.cf: cyrus_destination_recipient_limit=1
#
#cyrus unix - n n - - pipe
# user=cyrus argv=/cyrus/bin/deliver -e -r ${sender} -m ${extension} ${user}
#
# ====================================================================
# Old example of delivery via Cyrus.
#
#old-cyrus unix - n n - - pipe
# flags=R user=cyrus argv=/cyrus/bin/deliver -e -m ${extension} ${user}
#
# ====================================================================
#
# See the Postfix UUCP_README file for configuration details.
#
uucp unix - n n - - pipe
flags=Fqhu user=uucp argv=uux -r -n -z -a$sender - $nexthop!rmail ($recipient)
#
# Other external delivery methods.
#
ifmail unix - n n - - pipe
flags=F user=ftn argv=/usr/lib/ifmail/ifmail -r $nexthop ($recipient)
bsmtp unix - n n - - pipe
flags=Fq. user=bsmtp argv=/usr/lib/bsmtp/bsmtp -t$nexthop -f$sender $recipient
scalemail-backend unix - n n - 2 pipe
flags=R user=scalemail argv=/usr/lib/scalemail/bin/scalemail-store ${nexthop} ${user} ${extension}
mailman unix - n n - - pipe
flags=FR user=list argv=/usr/lib/mailman/bin/postfix-to-mailman.py
${nexthop} ${user}
spamassassin unix - n n - - pipe
flags=DROhu user=vmail:vmail argv=/usr/bin/spamc -f -e /usr/local/v2_mail/v2/script/v2_lda.sh ${sender} ${user}@${nexthop}
dovecot unix - n n - - pipe
flags=DRhu user=vmail:vmail argv=/usr/lib/dovecot/deliver -f ${sender} -d ${user}@${nexthop}
