Email server with no smtp connection

Terry asked:

Ubuntu 18.04 on Google Compute
Dovecot + postfix

I figure I should be able to connect to a port other than 465/587, and since I can relay all email through google there should be no issue with this method for an email server. Also Google says they put in a setting to allow connection to 465/587 so I should have no issues at all

when I try to telnet to the 2 ports I have postfix listening on (5001 & 8080, 8080 is only for testing) this is what I get in tcpdump

21:42:02.843771 IP h***-***-***-***.wtfrwi.dsl.dynamic.tds.net.46208 > mailserv1.c.enterprise-210914.internal.urd: Flags [S], seq 1961371525, win 29200, options [mss 1460,sackOK,TS val 240062507 ecr 0,nop,wscale 7], length 0
21:42:02.843831 IP mailserv1.c.enterprise-210914.internal.urd > h***.***.***.***.wtfrwi.dsl.dynamic.tds.net.46208: Flags [R.], seq 0, ack 1961371526, win 0, length 0

mail.log does not show anything for smtp connection on either port

The server can send email just fine, it is simply a matter of other applications connecting to this server to send email through the relay

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)
# ==========================================================================
#587      inet  n       -       y       -       -       smtpd
8080     inet     n     -     y     -     -     smtpd
#smtps  inet    n       -       n       -       -       smtpd
5001    inet    n       -       n       -       -       smtpd
#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=$mua_sender_restrictions
#  -o smtpd_recipient_restrictions=
#  -o smtpd_relay_restrictions=permit_sasl_authenticated,reject
#  -o milter_macro_daemon_name=ORIGINATING
#smtps     inet  n       -       n       -       -       smtpd
5001    inet    n       -       n       -       -       smtpd
#  -o syslog_name=postfix/smtps
  -o smtpd_tls_wrappermode=yes
  -o smtpd_sasl_auth_enable=yes
#  -o smtpd_reject_unlisted_recipient=no
  -o smtpd_client_restrictions=permit_sasl_authenticated,reject
#  -o smtpd_helo_restrictions=$mua_helo_restrictions
#  -o smtpd_sender_restrictions=$mua_sender_restrictions
#  -o smtpd_recipient_restrictions=
#  -o smtpd_relay_restrictions=permit_sasl_authenticated,reject
  -o milter_macro_daemon_name=ORIGINATING
#628       inet  n       -       y       -       -       qmqpd
pickup    unix  n       -       y       60      1       pickup
cleanup   unix  n       -       y       -       0       cleanup
qmgr      unix  n       -       n       300     1       qmgr
#qmgr     unix  n       -       n       300     1       oqmgr
tlsmgr    unix  -       -       y       1000?   1       tlsmgr
rewrite   unix  -       -       y       -       -       trivial-rewrite
bounce    unix  -       -       y       -       0       bounce
defer     unix  -       -       y       -       0       bounce
trace     unix  -       -       y       -       0       bounce
verify    unix  -       -       y       -       1       verify
flush     unix  n       -       y       1000?   0       flush
proxymap  unix  -       -       n       -       -       proxymap
proxywrite unix -       -       n       -       1       proxymap
smtp      unix  -       -       y       -       -       smtp
relay     unix  -       -       y       -       -       smtp
        -o syslog_name=postfix/$service_name
#       -o smtp_helo_timeout=5 -o smtp_connect_timeout=5
showq     unix  n       -       y       -       -       showq
error     unix  -       -       y       -       -       error
retry     unix  -       -       y       -       -       error
discard   unix  -       -       y       -       -       discard
local     unix  -       n       n       -       -       local
virtual   unix  -       n       n       -       -       virtual
lmtp      unix  -       -       y       -       -       lmtp
anvil     unix  -       -       y       -       1       anvil
scache    unix  -       -       y       -       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}

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 = webserver.com
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/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

### https://sealedabstract.com/code/nsa-proof-your-e-mail-in-2-hours/ ### Guide for below

smtpd_tls_cert_file=/etc/letsencrypt/live/webserver.com/fullchain.pem
smtpd_tls_key_file=/etc/letsencrypt/live/webserver.com/privkey.pem
smtpd_use_tls=yes
smtpd_tls_auth_only = yes
smtp_tls_security_level = may
smtp_tls_loglevel = 2
smtpd_tls_received_header = yes

smtpd_sasl_type = dovecot
smtpd_sasl_path = private/auth
smtpd_sasl_auth_enable = yes

smtpd_recipient_restrictions =
        permit_sasl_authenticated,
        permit_mynetworks,
        reject_unauth_destination



# See /usr/share/doc/postfix/TLS_README.gz in the postfix-doc package for
# information on enabling SSL in the smtp client.

smtpd_relay_restrictions = permit_mynetworks permit_sasl_authenticated defer_unauth_destination
myhostname = webserver.com
alias_maps = hash:/etc/aliases
alias_database = hash:/etc/aliases
myorigin = /etc/mailname
mydestination = localhost
relayhost = [smtp-relay.gmail.com]:587
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 = ipv4
# Force ehlo behavior
smtp_always_send_ehlo = yes
smtp_helo_name = webserver.com
virtual_transport = lmtp:unix:private/dovecot-lmtp
virtual_mailbox_domains = mysql:/etc/postfix/mysql-virtual-mailbox-domains.cf
virtual_mailbox_maps = mysql:/etc/postfix/mysql-virtual-mailbox-maps.cf
virtual_alias_maps = mysql:/etc/postfix/mysql-virtual-alias-maps.cf
local_recipient_maps = $virtual_mailbox_maps

inet_interfaces was set to loopback only, changing that to all allows me to telnet to the port with successful connection. Trying to connect to my server on that port times out now.

output of ss -l

udp   UNCONN  37632   0                                     127.0.0.53%lo:domain                     0.0.0.0:*     
udp   UNCONN  0       0                                   10.128.0.2%ens4:bootpc                     0.0.0.0:*     
udp   UNCONN  0       0                                         127.0.0.1:323                        0.0.0.0:*     
udp   UNCONN  0       0                                             [::1]:323                           [::]:*     
tcp   LISTEN  0       128                                         0.0.0.0:ssh                        0.0.0.0:*     
tcp   LISTEN  0       100                                         0.0.0.0:imaps                      0.0.0.0:*     
tcp   LISTEN  0       128                                       127.0.0.1:5572                       0.0.0.0:*     
tcp   LISTEN  0       100                                       127.0.0.1:smtp                       0.0.0.0:*     
tcp   LISTEN  0       80                                        127.0.0.1:mysql                      0.0.0.0:*     
tcp   LISTEN  0       100                                       127.0.0.1:http-alt                   0.0.0.0:*     
tcp   LISTEN  0       128                                   127.0.0.53%lo:domain                     0.0.0.0:*     
tcp   LISTEN  0       128                                            [::]:ssh                           [::]:*     
tcp   LISTEN  0       128                                               *:https                            *:*     
tcp   LISTEN  0       100                                            [::]:imaps                         [::]:*     
tcp   LISTEN  0       128                                               *:http                             *:*  

netstat -lpn -A inet

[email protected]:~# netstat -lpn -A inet
Active Internet connections (only servers)
Proto Recv-Q Send-Q Local Address           Foreign Address         State       PID/Program name    
tcp        0      0 0.0.0.0:22              0.0.0.0:*               LISTEN      1060/sshd           
tcp        0      0 0.0.0.0:993             0.0.0.0:*               LISTEN      573/dovecot         
tcp        0      0 127.0.0.1:5572          0.0.0.0:*               LISTEN      623/rclone          
tcp        0      0 127.0.0.1:5001          0.0.0.0:*               LISTEN      954/master          
tcp        0      0 127.0.0.1:3306          0.0.0.0:*               LISTEN      703/mysqld          
tcp        0      0 127.0.0.1:8080          0.0.0.0:*               LISTEN      954/master          
tcp        0      0 127.0.0.53:53           0.0.0.0:*               LISTEN      424/systemd-resolve 
udp    40704      0 127.0.0.53:53           0.0.0.0:*                           424/systemd-resolve 
udp        0      0 10.128.0.2:68           0.0.0.0:*                           405/systemd-network 
udp        0      0 127.0.0.1:323           0.0.0.0:*                           628/chronyd         

iptables

[email protected]:~# iptables -L
Chain INPUT (policy ACCEPT)
target     prot opt source               destination         
sshguard   all  --  anywhere             anywhere            
Chain FORWARD (policy ACCEPT)
target     prot opt source               destination         
Chain OUTPUT (policy ACCEPT)
target     prot opt source               destination         
Chain sshguard (1 references)
target     prot opt source               destination

UFW is not installed

I am also able to do a “telnet localhost 8080 or 5001” and I am able to connect, which initially had me thinking it was a firewall issue. Although seeing tcpdump receive a packet on my tests to telnet or nmap from the outside world made me think the firewall was not an issue.

Although this is google VPC network firewall, yes I do have rules in to allow 465,587,5001,8080 for tcp and udp. I can confirm that it effects the instance by going in to the specific firewall rule to see which instances are being affected by that rule. This is done utilizing the smtp tag for reference. Firewall rules are as follows

allow-smtp
Description
smtp ports
Network
default
Priority
1000
Direction
Ingress
Action on match
Allow
Targets
Target tags
smtp
Source filters
IP ranges
0.0.0.0/0
Protocols and ports
tcp:587
udp:587
tcp:465
udp:465
tcp:5001
udp:5001
tcp:8080
udp:8080
Enforcement
Enabled
Applicable to instances
Name    Internal IP Tags    Service accounts    Project Network details
mailserv1   10.128.0.2  http-server, https-server,      

Any help would be greatly appreciated. Seeing the packets come in tells me the port is open, even though telnet and nmap say it is blocked.

It appears the ack packet is unable to return, in whichcase I was thinking a static route may be needed, although I have not been able to succeed just yet. Thank you for any help.

My answer:


Your listeners are listening only for connections from the local host.

tcp        0      0 127.0.0.1:5001          0.0.0.0:*               LISTEN      954/master          
tcp        0      0 127.0.0.1:8080          0.0.0.0:*               LISTEN      954/master          

This is because Postfix has been specifically configured to listen only for local connections.

inet_interfaces = loopback-only

To resolve the problem, tell Postfix to accept outside connections.

inet_interfaces = all

View the full question and any other answers on Server Fault.

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