postfix – Fixing Postfix Can’t Connect from SMTP with TLS

Thanks all for helping me :),i was working a direct bulk mail sender project,
my program was running properly then it gave me an error then i've spend too much time with a lot of searching from articles i did debug (very low level ) in last 2 days(im asleep).
problem causing this from little thing "str(email)" email represents sender list(for bulking diffrent accounts) and its supposed to be a list not a str :/, it take soooo much time but in this journey i've learned a lot of cool things 🙂
shortly : dont be afraid to make little mistakes

i can connect with external openssl but couldnt with telnet(on mail.example.com:587)

openssl s_client -starttls smtp -connect mail.example.com:587

after i execute starttls in smtp connection closed by foreign host

mail.log

Dec  6 15:45:45 example postfix/submission/smtpd[5149]: connect from unknown[********]
Dec  6 15:45:57 example postfix/submission/smtpd[5149]: SSL_accept error from unknown[********]: -1
Dec  6 15:45:57 example postfix/submission/smtpd[5149]: warning: TLS **library problem: error:1408F10B:SSL routines:ssl3_get_record:wrong version number:../ssl/record/ssl3_record.c:252:**
Dec  6 15:45:57 example postfix/submission/smtpd[5149]: lost connection after STARTTLS from unknown[*******]
Dec  6 15:45:57 example postfix/submission/smtpd[5149]: disconnect from unknown[*********] ehlo=1 starttls=0/1 commands=1/2

postconf -n

alias_database = hash:/etc/aliases
alias_maps = hash:/etc/aliases
command_directory = /usr/sbin
compatibility_level = 2
daemon_directory = /usr/lib/postfix/sbin
data_directory = /var/lib/postfix
debugger_command = PATH=/bin:/usr/bin:/usr/local/bin:/usr/X11R6/bin ddd $daemon_directory/$process_name $process_id & sleep 5
home_mailbox = Maildir/
inet_interfaces = all
inet_protocols = all
local_recipient_maps = unix:passwd.byname $alias_maps
mailbox_size_limit = 0
milter_default_action = accept
milter_protocol = 2
mydestination = mail.example.com,example.com, localhost,localhost.localdomain
mydomain = example.com
myhostname = mail.example.com
mynetworks = 168.100.189.0/28, 127.0.0.0/8,***.**.***.**/25
myorigin = /etc/mailname
newaliases_path = /usr/bin/newaliases
non_smtpd_milters = inet:localhost:12301
recipient_delimiter = +
sendmail_path = /usr/sbin/postfix
setgid_group = postdrop
smtp_tls_ciphers = high
smtp_tls_protocols = !SSLv2, !SSLv3
smtp_use_tls = yes
smtpd_banner = $myhostname ESMTP $mail_name (Ubuntu)
smtpd_helo_required = yes
smtpd_helo_restrictions = permit_mynetworks, reject_non_fqdn_helo_hostname, reject_invalid_helo_hostname, permit
smtpd_milters = inet:localhost:12301
smtpd_sasl_auth_enable = yes
smtpd_sasl_local_domain = $mydomain
smtpd_sasl_path = auth/dovecot
smtpd_sasl_security_options = noanonymous
smtpd_sasl_type = dovecot
smtpd_tls_cert_file = /etc/postfix/cert-20181202-231932.pem
smtpd_tls_ciphers = high
smtpd_tls_key_file = /etc/postfix/key-20181202-231932.pem
smtpd_tls_loglevel = 1
smtpd_tls_protocols = !SSLv2, !SSLv3
smtpd_tls_received_header = yes
smtpd_tls_security_level = may
smtputf8_enable = yes
tls_random_source = dev:/dev/urandom
unknown_local_recipient_reject_code = 550
virtual_alias_maps = hash:/etc/postfix/virtual

master.cf

smtp        inet  n       -       y       -       -       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
submission inet n       -       -       -       -       smtpd
  -o syslog_name=postfix/submission
  -o smtpd_tls_wrappermode=no
  #-o smtpd_tls_security_level=encrypt
  -o smtpd_sasl_auth_enable=yes
  -o smtpd_recipient_restrictions=permit_mynetworks,permit_sasl_authenticated,reject
  -o milter_macro_daemon_name=ORIGINATING
  -o smtpd_sasl_type=dovecot
#  -o smtpd_sasl_path = auth/dovecot
  -o smtpd_sasl_path=private/auth

#  -o smtpd_sender_restrictions=$mua_sender_restrictions
#  -o smtpd_recipient_restrictions= permit_mynetworks,permit_sasl_authenticated,reject
#  -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

dovecot.conf

disable_plaintext_auth = no
mail_privileged_group = mail
mail_location = maildir:~/Maildir
auth_mechanisms = plain
auth_username_format ="%Ln"
userdb {
  driver = passwd
}
passdb {
  args = %s
  driver = pam
}
protocols = " imap"


protocol imap {
  mail_plugins = " auto"
}
plugin {
  autocreate = Trash
  autocreate2 = Sent
  autosubscribe = Trash
  autosubscribe2 = Sent
}
service auth {
  unix_listener /var/spool/postfix/private/auth {
    group = postfix
    mode = 0660
    user = postfix
  }
}
listen = *
ssl=yes
ssl_cert = </etc/postfix/cert-20181202-231932.pem
ssl_key = </etc/postfix/key-20181202-231932.pem

netstat

netstat --proto=inet -pnl | grep 587
tcp        0      0 0.0.0.0:587             0.0.0.0:*               LISTEN      5073/master  

openssl s_client -starttls smtp -connect mail.example.com:587

CONNECTED(00000003)
depth=0 C = AU, ST = Some-State, O = Internet Widgits Pty Ltd
verify error:num=18:self signed certificate
verify return:1
depth=0 C = AU, ST = Some-State, O = Internet Widgits Pty Ltd
verify return:1
---
Certificate chain
 0 s:/C=AU/ST=Some-State/O=Internet Widgits Pty Ltd
   i:/C=AU/ST=Some-State/O=Internet Widgits Pty Ltd
---
Server certificate
-----BEGIN CERTIFICATE-----
******************************
-----END CERTIFICATE-----
subject=/C=AU/ST=Some-State/O=Internet Widgits Pty Ltd
issuer=/C=AU/ST=Some-State/O=Internet Widgits Pty Ltd
---
No client certificate CA names sent
Peer signing digest: SHA512
Server Temp Key: X25519, 253 bits
---
SSL handshake has read 2531 bytes and written 302 bytes
Verification error: self signed certificate
---
New, TLSv1.2, Cipher is ECDHE-RSA-AES256-GCM-SHA384
Server public key is 4096 bit
Secure Renegotiation IS supported
Compression: NONE
Expansion: NONE
No ALPN negotiated
SSL-Session:
    Protocol  : TLSv1.2
    Cipher    : ECDHE-RSA-AES256-GCM-SHA384
    Session-ID: E34DC2BC95BF207D4B5E38C6FABD2A25AC43290A994C50C7AEC183CA224A31D2
    Session-ID-ctx: 
    Master-Key: 0413A1112B664D6FA2EA348D70F6614AF5567338F0C61FDDC62030DC24A9C7719332CE322960AC5DD1D84A1205E2B0B9
    PSK identity: None
    PSK identity hint: None
    SRP username: None
    TLS session ticket lifetime hint: 7200 (seconds)
    TLS session ticket:
    0000 - 97 4c 40 cf ae aa cc f3-32 80 52 0d fe 9f c0 da   .L@.....2.R.....
    0010 - a5 b8 3f 3c 0d ae 29 a7-88 b4 c1 6b 65 bf 38 e0   ..?<..)....ke.8.
    0020 - cc f9 05 93 43 4f 60 d4-a2 0f 3e 27 88 3e 13 1b   ....CO`...>'.>..
    0030 - 6a 31 01 86 5a 83 4c 80-a4 c4 5f 6b 6c bb ee e6   j1..Z.L..._kl...
    0040 - 5c 02 71 e1 2f 1e 96 38-4c 58 65 02 2e 89 78 96   \.q./..8LXe...x.
    0050 - 45 a6 b5 0c b4 b5 b6 61-65 c5 43 37 8d 4c 82 99   E......ae.C7.L..
    0060 - 88 2f 48 98 ce 9a 68 35-d8 1a b8 86 ff 3b ce 15   ./H...h5.....;..
    0070 - 0e e2 fd 02 60 07 1b 2a-2c 6d 0d 3b 32 25 f9 0d   ....`..*,m.;2%..
    0080 - d6 f8 31 2f 04 88 84 c9-bb 98 b3 fa ee 72 bd c1   ..1/.........r..
    0090 - 75 29 31 29 cb 68 99 36-49 77 4e 4a 07 71 ed 6c   u)1).h.6IwNJ.q.l
    00a0 - 20 88 c3 4d f3 d1 1c 3e-a4 16 7a 53 53 8b 51 17    ..M...>..zSS.Q.

    Start Time: 1544115275
    Timeout   : 7200 (sec)
    Verify return code: 18 (self signed certificate)
    Extended master secret: yes
---
250 

telnet mail.example.com 587

Connected to mail.example.com.
Escape character is '^]'.
220 mail.example.com ESMTP Postfix (Ubuntu)
ehlo mail.example.com
250-mail.example.com
250-PIPELINING
250-SIZE 10240000
250-VRFY
250-ETRN
250-STARTTLS
250-AUTH PLAIN
250-ENHANCEDSTATUSCODES
250-8BITMIME
250-DSN
250 SMTPUTF8
starttls
220 2.0.0 Ready to start TLS
auth plain AHJvb3QAZXhhbXBsZXBhc3M=
Connection closed by foreign host.