I have a postfix email server (mx) in a docker container on a host. My MX only receives emails (SMTPD). My goal is to receive emails from gmail on port 587 so that TLS is always enforced. However, I can only receive emails from gmail if port 25 is open. As an independent way to check encrypted SMTPD (ESMTPD), I am using openssl s_client to send emails as well.
Here are my inbound firewall rules on the host when both ports 25 and 587 are open.
Here is my docker-compose.yml when both ports 25 and 587 are open:
services:
mailserver:
# More information about the mail-server ports:
# https://docker-mailserver.github.io/docker-mailserver/edge/config/security/understanding-the-ports/
# To avoid conflicts with yaml base-60 float, DO NOT remove the quotation marks.
ports:
- '25:25' # SMTP (temporarily opened for troubleshooting)
- '587:587' # ESMTP (explicit TLS => STARTTLS)
Here is my postfix/main.cf.
# See /usr/share/postfix/main.cf.dist for a commented, more complete version
# Debian specific: Specifying a file name will cause the first
# line of that file to be used as the name. The Debian default
# is /etc/mailname.
#myorigin = /etc/mailname
smtpd_banner = $myhostname ESMTP $mail_name (Ubuntu)
biff = no
# appending .domain is the MUA's job.
append_dot_mydomain = no
# Uncomment the next line to generate "delayed mail" warnings
#delay_warning_time = 4h
readme_directory = no
# See http://www.postfix.org/COMPATIBILITY_README.html -- default to 2 on
# fresh installs.
compatibility_level = 2
# TLS parameters
smtpd_tls_cert_file = /etc/letsencrypt/live/mail.example.com/fullchain.pem
smtpd_tls_key_file = /etc/letsencrypt/live/mail.example.com/privkey.pem
smtpd_tls_security_level = encrypt
smtp_tls_CApath=/etc/ssl/certs
smtp_tls_security_level=may
smtp_tls_session_cache_database = btree:${data_directory}/smtp_scache
smtpd_relay_restrictions = permit_mynetworks permit_sasl_authenticated defer_unauth_destination
myhostname = mail
alias_maps = hash:/etc/aliases
alias_database = hash:/etc/aliases
mydestination = mail.example.com, example.com, localhost.example.com, localhost.localdomain, localhost
relayhost =
mynetworks = 127.0.0.0/8 [::ffff:127.0.0.0]/104 [::1]/128
mailbox_size_limit = 0
recipient_delimiter = +
inet_interfaces = all
inet_protocols = all
maillog_file = /var/log/mail.log
myorigin = example.com
home_mailbox = Maildir/
Here is my Here is my 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" or
# on-line: http://www.postfix.org/master.5.html).
#
# Do not forget to execute "postfix reload" after editing this file.
#
# ==========================================================================
# service type private unpriv chroot wakeup maxproc command + args
# (yes) (yes) (no) (never) (100)
# ==========================================================================
#smtp inet n - y - 1 postscreen
#smtpd pass - - y - - smtpd
#dnsblog unix - - y - 0 dnsblog
#tlsproxy unix - - y - 0 tlsproxy
#submission inet n - y - - smtpd
# -o syslog_name=postfix/submission
# -o smtpd_tls_security_level=encrypt
# -o smtpd_sasl_auth_enable=yes
# -o smtpd_tls_auth_only=yes
# -o smtpd_reject_unlisted_recipient=no
# -o smtpd_client_restrictions=$mua_client_restrictions
# -o smtpd_helo_restrictions=$mua_helo_restrictions
# -o smtpd_sender_restrictions=$mua_sender_restrictions
# -o smtpd_recipient_restrictions=
# -o smtpd_relay_restrictions=permit_sasl_authenticated,reject
# -o milter_macro_daemon_name=ORIGINATING
#smtps inet n - y - - smtpd
# -o syslog_name=postfix/smtps
# -o smtpd_tls_wrappermode=yes
# -o smtpd_sasl_auth_enable=yes
# -o smtpd_reject_unlisted_recipient=no
# -o smtpd_client_restrictions=$mua_client_restrictions
# -o smtpd_helo_restrictions=$mua_helo_restrictions
# -o smtpd_sender_restrictions=$mua_sender_restrictions
# -o smtpd_recipient_restrictions=
# -o smtpd_relay_restrictions=permit_sasl_authenticated,reject
# -o milter_macro_daemon_name=ORIGINATING
#628 inet n - y - - qmqpd
smtp inet n - n - - smtpd
pickup unix n - n 60 1 pickup
cleanup unix n - n - 0 cleanup
#qmgr unix n - n 300 1 oqmgr
qmgr unix n - n 300 1 qmgr
tlsmgr unix - - n 1000? 1 tlsmgr
rewrite unix - - n - - trivial-rewrite
bounce unix - - n - 0 bounce
defer unix - - n - 0 bounce
trace unix - - n - 0 bounce
verify unix - - n - 1 verify
flush unix n - n 1000? 0 flush
proxymap unix - - n - - proxymap
proxywrite unix - - n - 1 proxymap
smtp unix - - n - - smtp
# -o smtp_helo_timeout=5 -o smtp_connect_timeout=5
relay unix - - n - - smtp
-o syslog_name=postfix/$service_name
showq unix n - n - - showq
error unix - - n - - error
retry unix - - n - - error
discard unix - - n - - discard
local unix - n n - - local
virtual unix - n n - - virtual
lmtp unix - - n - - lmtp
anvil unix - - n - 1 anvil
scache unix - - n - 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
#
postlog unix-dgram n - n - 1 postlogd
#
# ====================================================================
#
# 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.
#
maildrop unix - n n - - pipe flags=DRhu
user=vmail argv=/usr/bin/maildrop -d ${recipient}
#
# Other external delivery methods.
#
uucp unix - n n - - pipe flags=Fqhu
user=uucp argv=uux -r -n -z -a$sender - $nexthop!rmail ($recipient)
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}
${user}
submission inet n - n - - smtpd
-o syslog_name=postfix/submission
-o smtpd_tls_security_level=encrypt
Using openssl s_client, I can receive an email on my MX when only port 587 is open.
kfike@pop-os:~$ openssl s_client -starttls smtp -ign_eof -crlf -connect mail.example.com:587
CONNECTED(00000003)
read R BLOCK
ehlo mail.example.com
250-mail
250-PIPELINING
250-SIZE 10240000
250-VRFY
250-ETRN
250-ENHANCEDSTATUSCODES
250-8BITMIME
250-DSN
250-SMTPUTF8
250 CHUNKING
MAIL FROM: <[email protected]>
250 2.1.0 Ok
RCPT TO: <[email protected]>
250 2.1.5 Ok
data
354 End data with <CR><LF>.<CR><LF>
Subject: 24022801 openssl 587
24022801 openssl 587
.
250 2.0.0 Ok: queued as 484164047A
quit
221 2.0.0 Bye
closed
When I open port 25 on the host and the container, I receive all the emails I had previously sent when port 25 was closed:
sage-mailserver | Feb 28 03:38:18 prod postfix/smtpd[225]: connect from mail-io1-f47.google.com[209.85.166.47]
sage-mailserver | Feb 28 03:38:18 prod postfix/smtpd[225]: D5AED40485: client=mail-io1-f47.google.com[209.85.166.47]
sage-mailserver | Feb 28 03:38:18 prod postfix/cleanup[266]: D5AED40485: message-id=<CAG3XwjSVnRON0o7ku58uTCPkFxywounaJYbPfUZ_S30MNQ8NRQ@mail.gmail.com>
sage-mailserver | Feb 28 03:38:18 prod postfix/qmgr[175]: D5AED40485: from=<[email protected]>, size=2923, nrcpt=1 (queue active)
sage-mailserver | Feb 28 03:38:18 prod postfix/local[267]: D5AED40485: to=<[email protected]>, relay=local, delay=0.02, delays=0.01/0.01/0/0, dsn=2.0.0, status=sent (delivered to maildir)
sage-mailserver | Feb 28 03:38:18 prod postfix/qmgr[175]: D5AED40485: removed
sage-mailserver | Feb 28 03:38:18 prod postfix/smtpd[225]: disconnect from mail-io1-f47.google.com[209.85.166.47] ehlo=2 starttls=1 mail=1 rcpt=1 bdat=1 quit=1 commands=7
sage-mailserver | Feb 28 03:38:53 prod postfix/smtpd[225]: connect from mail-qt1-f176.google.com[209.85.160.176]
sage-mailserver | Feb 28 03:38:53 prod postfix/smtpd[225]: E1E1640485: client=mail-qt1-f176.google.com[209.85.160.176]
sage-mailserver | Feb 28 03:38:53 prod postfix/cleanup[266]: E1E1640485: message-id=<CAG3XwjRC0NyH0qej3EhGTz8YvhbiBLUTVB-NF6ZaaUAwcwmqXg@mail.gmail.com>
sage-mailserver | Feb 28 03:38:53 prod postfix/qmgr[175]: E1E1640485: from=<[email protected]>, size=2917, nrcpt=1 (queue active)
sage-mailserver | Feb 28 03:38:53 prod postfix/local[267]: E1E1640485: to=<[email protected]>, relay=local, delay=0.02, delays=0.01/0/0/0.01, dsn=2.0.0, status=sent (delivered to maildir)
sage-mailserver | Feb 28 03:38:53 prod postfix/qmgr[175]: E1E1640485: removed
sage-mailserver | Feb 28 03:38:53 prod postfix/smtpd[225]: disconnect from mail-qt1-f176.google.com[209.85.160.176] ehlo=2 starttls=1 mail=1 rcpt=1 bdat=1 quit=1 commands=7
sage-mailserver | Feb 28 03:40:23 prod postfix/smtpd[225]: connect from mail-qk1-f177.google.com[209.85.222.177]
sage-mailserver | Feb 28 03:40:23 prod postfix/smtpd[225]: E8BB740485: client=mail-qk1-f177.google.com[209.85.222.177]
sage-mailserver | Feb 28 03:40:23 prod postfix/cleanup[266]: E8BB740485: message-id=<CAG3XwjTxJwQQaCWXjzCD5jg73=6+jEJNWXXj7oF1AqbTnN81ag@mail.gmail.com>
sage-mailserver | Feb 28 03:40:23 prod postfix/qmgr[175]: E8BB740485: from=<[email protected]>, size=2920, nrcpt=1 (queue active)
sage-mailserver | Feb 28 03:40:23 prod postfix/local[267]: E8BB740485: to=<[email protected]>, relay=local, delay=0.01, delays=0.01/0/0/0, dsn=2.0.0, status=sent (delivered to maildir)
In summary:
| Open Port(s) | Client | Email received? |
| ------------ | ------ | -------------- |
| 25 and 587 | openssl s_client | Yes |
| 25 and 587 | gmail | Yes |
| 587 | openssl s_client | Yes |
| 587 | gmail | No |
Any ideas as why I can't receive emails from gmail when only port 587 is open and not port 25? Thanks so much for any insights!