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Joined: 09 Sep 2008
Posts: 529

PostPosted: Sat May 03, 2014 7:22 pm    Post subject: Postfix security Reply with quote

As a learning experience, I am trying to set up an email server. I followed the guide at I can send mail locally, but when I try to send messages to my GMail account, mail.log says something like this:

myhostname postfix/smtp[18284]: connect to[]:25: Connection timed out

I tried setting a relayhost in, but it still shows a similar message:

myhostname postfix/smtp[18148]: AAC9BC3925: to=<>, relay=none, delay=30, delays=0.02/0/30/0, dsn=4.4.1, status=deferred (connect to[]:25: Connection timed out

A likely possibility, based on what I have read, is that my I.S.P. blocks port 25. I think that I read this in their documentation, as well. I trying telnetting into port 587 and sending a message, but I still got the same messages in mail.log.


myhostname =
mydomain =
soft_bounce = yes
queue_directory = /var/spool/postfix
command_directory = /usr/sbin
daemon_directory = /usr/libexec/postfix
data_directory = /var/lib/postfix
mail_owner = postfix
unknown_local_recipient_reject_code = 550
mynetworks_style = host
recipient_delimiter = +
debug_peer_level = 2
debugger_command =
    ddd $daemon_directory/$process_name $process_id & sleep 5
sendmail_path = /usr/sbin/sendmail
newaliases_path = /usr/bin/newaliases
mailq_path = /usr/bin/mailq
setgid_group = postdrop
html_directory = no
manpage_directory = /usr/share/man
sample_directory = /etc/postfix
readme_directory = no
inet_protocols = ipv4
home_mailbox = .maildir/


smtp      inet  n       -       n       -       -       smtpd
submission inet n       -       n       -       -       smtpd
  -o syslog_name=postfix/submission
  -o smtpd_tls_security_level=encrypt
  -o smtpd_sasl_auth_enable=yes
#smtps     inet  n       -       n       -       -       smtpd
pickup    unix  n       -       n       60      1       pickup
cleanup   unix  n       -       n       -       0       cleanup
qmgr      unix  n       -       n       300     1       qmgr
#qmgr     unix  n       -       n       300     1       oqmgr
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

I tried changing smtp to use port 587 using /etc/services and restarted postfix, but I got the same message, just with port 587 instead of 25. The ports are open in my firewall. At this point, I feel a bit like I'm not sure that I know what I'm doing, and would appreciate some help.

Last edited by keet on Sat May 17, 2014 8:29 pm; edited 1 time in total
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Joined: 09 Sep 2008
Posts: 529

PostPosted: Wed May 07, 2014 1:15 am    Post subject: Reply with quote

I'm not sure why people are not replying, but maybe it's because of this post:

I wondering whether switching to a business account would help at all. It looks like I.S.P.s around here block 25 for residential, but only rarely and on a case-by-case basis for business accounts.
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Joined: 09 Sep 2008
Posts: 529

PostPosted: Sat May 17, 2014 12:49 am    Post subject: Reply with quote

Ok, I made it work, sort of. I got a V.P.S. and set up Postfix, but it's in CentOS. Oh, well, at least I have a working email server. I am a bit paranoid about security, and I want to make sure that it's all encrypted whenever possible. I've tested this using Wireshark and Tcpdump, and as far as I can tell, all transmissions are encrypted, but is there any way that I could know for sure from /var/log/maillog?

dovecot: imap-login: Login: user=<notmyusername>, method=PLAIN, rip=notmyremoteaddress, lip=notmyserveraddress, mpid=4925, TLS

I'd assume that TLS means it's encrypted using T.L.S.while logging in to check my mail, even though it's PLAIN authentication, right?

setting up TLS connection to someremotemailserver[theiripaddress]:25
Untrusted TLS connection established to srms[tipa]:25: TLSv1.2 with cipher AES128-SHA256 (128/128 bits)

This means the outgoing mail transmission looks encrypted, but my mail server doesn't trust its certificate issuer?

However, one thing that I don't see is any mention of encryption when I GET messages from another domain. On the other hand, if I run

tcpdump -A -vvv -s 0 -i eth0 > test.txt
while sending a message from my GMail account to my server and then search for any trace of text from the incoming message, I don't see it. However, I do see a STARTTLS command and what looks like certificate negotiation. Thus, it looks like it's encrypted, right? Unless I'm not using tcpdump properly or it's missing something...
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