Can't connect to a postfix server though port 25 is open

Question

I'm trying to connect via outlook to a postfix server (send example message via smtp). On the server it seems the port is open:

 nmap -sT -O localhost

Starting Nmap 6.40 ( http://nmap.org ) at 2016-09-24 15:23 EDT
Nmap scan report for localhost (127.0.0.1)
Host is up (0.000046s latency).
Other addresses for localhost (not scanned): 127.0.0.1
rDNS record for 127.0.0.1: localhost.localdomain
Not shown: 990 closed ports
PORT      STATE SERVICE
21/tcp    open  ftp
22/tcp    open  ssh
25/tcp    open  smtp
80/tcp    open  http
110/tcp   open  pop3
143/tcp   open  imap
993/tcp   open  imaps
995/tcp   open  pop3s
3306/tcp  open  mysql
10000/tcp open  snet-sensor-mgmt
No exact OS matches for host (If you know what OS is running on it, see http://nmap.org/submit/ ).


Network Distance: 0 hops

OS detection performed. Please report any incorrect results at http://nmap.org/submit/ .
Nmap done: 1 IP address (1 host up) scanned in 12.06 seconds

but when I try to connect to the server via Outlook it seems it doesn't respond at all. Here is a telnet check I've made(hostname9727.com is defined in my host file):

C:\Users\A>telnet hostname9727.com 25
Connecting To hostname9727.com...Could not open connection to the host, on port 25: Connect failed

While with other ports like 110:

+OK Dovecot ready.

A connection is created

postconf -n

postconf -n

alias_database = hash:/etc/aliases home_mailbox = /home/virtual/mail/
alias_maps = hash:/etc/aliases
broken_sasl_auth_clients = yes
command_directory = /usr/sbin
config_directory = /etc/postfix
daemon_directory = /usr/libexec/postfix
data_directory = /var/lib/postfix
debug_peer_level = 2
debugger_command = PATH=/bin:/usr/bin:/usr/local/bin:/usr/X11R6/bin ddd $daemon_directory/$process_name $process_id & sleep 5
home_mailbox = /home/virtual/mail/
html_directory = no
inet_interfaces = localhost
inet_protocols = all
mail_owner = postfix
mailq_path = /usr/bin/mailq.postfix
manpage_directory = /usr/share/man
mydestination = $myhostname, localhost.$mydomain, localhost, $mydomain
mydomain = hostname9727.com
mynetworks = 127.0.0.0/8, 10.0.0.0/24
myorigin = $myhostname
newaliases_path = /usr/bin/newaliases.postfix
queue_directory = /var/spool/postfix
readme_directory = /usr/share/doc/postfix-2.10.1/README_FILES
sample_directory = /usr/share/doc/postfix-2.10.1/samples
sendmail_path = /usr/sbin/sendmail.postfix
setgid_group = postdrop
smtpd_banner = $myhostname ESMTP
unknown_local_recipient_reject_code = 550

postconf -M

smtp       inet  n       -       n       -       -       smtpd
pickup     unix  n       -       n       60      1       pickup
cleanup    unix  n       -       n       -       0       cleanup
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
relay      unix  -       -       n       -       -       smtp
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

Solution

Your postfix server is configured to be reachable on the loopback interface only, as witnessed by the postconf output line:

inet_interfaces = localhost

If you want it to be reachable from other hosts you need to change that configuration by entering:

sudo postconf -e "inet_interfaces = all"

Comments

[prognoza]

I did those changes, yet, I'm not table to connect to the relevant port. nmap -sT -O hostname9727.com Starting Nmap 6.40 ( nmap.org ) at 2016-09-25 23:39 EDT Nmap scan report for hostname9727.com (31.220.108.9) Host is up (0.000059s latency). Not shown: 990 closed ports PORT STATE SERVICE 21/tcp open ftp 22/tcp open ssh 80/tcp open http 110/tcp open pop3 143/tcp open imap 993/tcp open imaps 995/tcp open pop3s 3306/tcp open mysql 10000/tcp open snet-sensor-mgmt 33354/tcp open unknown Thanks!

[Tilman Schmidt]

nmap isn't the optimal tool for diagnosing this. First check your config again to see whether it now says inet_interfaces = all. Also make sure to restart the postfix service after changing the config. Then check which address the postfix master process actually listens on with netstat -antp, and check whether you can connect to port 25 on the external address from the server itself with telnet 31.220.108.9 25.