title: SMTP docker-container not sending emails
body: <p>I created a group of docker containers to run a web app (Python/Django). One of them is smtp-server:</p>
  <pre><code>smtp:
      image: namshi/smtp:latest
      networks:
        - nginx_ext_network
      environment:
        MAILNAME: 'mailer'
      restart: always
      ports:
        - &quot;25:25&quot;
  </code></pre>
  <p>But when the web app needs to send an email, smtp server tries to do it, but fails.
  I tried it multiple times, with different ports and with different emails. Nothing works.</p>
  <p>LOGS for smtp-container:</p>
  <pre><code>+ sed -ri '
      s/^#?(dc_local_interfaces)=.*/\1='\''[0.0.0.0]:25 ; [::0]:25'\''/;
      s/^#?(dc_other_hostnames)=.*/\1='\'''\''/;
      s/^#?(dc_relay_nets)=.*/\1='\''172.19.0.2\/16'\''/;
      s/^#?(dc_eximconfig_configtype)=.*/\1='\''internet'\''/;
  ' /etc/exim4/update-exim4.conf.conf
  + update-exim4.conf -v
  using non-split configuration scheme from /etc/exim4/exim4.conf.template
      1 LOG: MAIN
      1   exim 4.89 daemon started: pid=1, -q15m, listening for SMTP on port 25 (IPv6 and IPv4)
    273 LOG: MAIN
    273   &lt;= webmaster@localhost H=mailer_apache_1.mailer_nginx_ext_network (83d1331a44cb) [172.19.0.3] P=esmtp S=2162 id=156606357503.34.13723816267095054951@83d1331a44cb
    273 LOG: smtp_connection MAIN
    273   SMTP connection from mailer_apache_1.mailer_nginx_ext_network (83d1331a44cb) [172.19.0.3] closed by QUIT
    274 Exim version 4.89 uid=101 gid=101 pid=274 D=40001
  Berkeley DB: Berkeley DB 5.3.28: (September  9, 2013)
  Support for: crypteq iconv() IPv6 GnuTLS move_frozen_messages DKIM DNSSEC Event OCSP PRDR SOCKS TCP_Fast_Open
  Lookups (built-in): lsearch wildlsearch nwildlsearch iplsearch cdb dbm dbmjz dbmnz dnsdb dsearch nis nis0 passwd
  Authenticators: cram_md5 plaintext
  Routers: accept dnslookup ipliteral manualroute queryprogram redirect
  Transports: appendfile/maildir/mailstore autoreply lmtp pipe smtp
  Fixed never_users: 0
  Configure owner: 0:0
  Size of off_t: 8
    274 delivering 1hz2fv-00004P-1K
    274 R: dnslookup for djangomailape@gmail.com
    275 T: remote_smtp for djangomailape@gmail.com
    275 Connecting to gmail-smtp-in.l.google.com [2a00:1450:4010:c08::1a]:25 ... failed: Cannot assign requested address
    275 LOG: MAIN
    275   H=gmail-smtp-in.l.google.com [2a00:1450:4010:c08::1a] Cannot assign requested address
    275 Connecting to gmail-smtp-in.l.google.com [64.233.165.27]:25 ... connected
    275   SMTP(close)&gt;&gt;
    275 LOG: MAIN
    275   H=gmail-smtp-in.l.google.com [64.233.165.27]: Remote host closed connection in response to initial connection
    275 Connecting to alt1.gmail-smtp-in.l.google.com [2404:6800:4008:c04::1a]:25 ... failed: Cannot assign requested address
    275 LOG: MAIN
    275   H=alt1.gmail-smtp-in.l.google.com [2404:6800:4008:c04::1a] Cannot assign requested address
    275 Connecting to alt1.gmail-smtp-in.l.google.com [74.125.204.27]:25 ... connected
    275   SMTP(close)&gt;&gt;
    275 LOG: MAIN
    275   H=alt1.gmail-smtp-in.l.google.com [74.125.204.27]: Remote host closed connection in response to initial connection
    275 Connecting to alt2.gmail-smtp-in.l.google.com [2607:f8b0:400e:c04::1b]:25 ... failed: Cannot assign requested address
    275 LOG: MAIN
    275   H=alt2.gmail-smtp-in.l.google.com [2607:f8b0:400e:c04::1b] Cannot assign requested address
    275 Connecting to alt3.gmail-smtp-in.l.google.com [2607:f8b0:4003:c09::1b]:25 ... failed: Cannot assign requested address
    275 LOG: MAIN
    275   H=alt3.gmail-smtp-in.l.google.com [2607:f8b0:4003:c09::1b] Cannot assign requested address
    275 Connecting to alt4.gmail-smtp-in.l.google.com [2607:f8b0:4001:c16::1b]:25 ... failed: Cannot assign requested address
    275 LOG: MAIN
    275   H=alt4.gmail-smtp-in.l.google.com [2607:f8b0:4001:c16::1b] Cannot assign requested address
    274 LOG: MAIN
    274   == djangomailape@gmail.com R=dnslookup T=remote_smtp defer (99): Cannot assign requested address H=alt1.gmail-smtp-in.l.google.com [74.125.204.27]
    276 LOG: MAIN
    276   &lt;= webmaster@localhost H=mailer_apache_1.mailer_nginx_ext_network (83d1331a44cb) [172.19.0.3] P=esmtp S=2187 id=156606361852.33.3228996691969512605@83d1331a44cb
    276 LOG: smtp_connection MAIN
    276   SMTP connection from mailer_apache_1.mailer_nginx_ext_network (83d1331a44cb) [172.19.0.3] closed by QUIT
    277 Exim version 4.89 uid=101 gid=101 pid=277 D=40001
  Berkeley DB: Berkeley DB 5.3.28: (September  9, 2013)
  Support for: crypteq iconv() IPv6 GnuTLS move_frozen_messages DKIM DNSSEC Event OCSP PRDR SOCKS TCP_Fast_Open
  Lookups (built-in): lsearch wildlsearch nwildlsearch iplsearch cdb dbm dbmjz dbmnz dnsdb dsearch nis nis0 passwd
  Authenticators: cram_md5 plaintext
  Routers: accept dnslookup ipliteral manualroute queryprogram redirect
  Transports: appendfile/maildir/mailstore autoreply lmtp pipe smtp
  Fixed never_users: 0
  Configure owner: 0:0
  Size of off_t: 8
    277 delivering 1hz2gc-00004S-H8
    277 R: dnslookup for eleriya-25@yandex.ru
    278 T: remote_smtp for eleriya-25@yandex.ru
    278 Connecting to mx.yandex.ru [2a02:6b8::89]:25 ... failed: Cannot assign requested address
    278 LOG: MAIN
    278   H=mx.yandex.ru [2a02:6b8::89] Cannot assign requested address
    278 Connecting to mx.yandex.ru [87.250.250.89]:25 ... connected
    278   SMTP(close)&gt;&gt;
    278 LOG: MAIN
    278   H=mx.yandex.ru [87.250.250.89]: Remote host closed connection in response to initial connection
    278 Connecting to mx.yandex.ru [213.180.193.89]:25 ... connected
    278   SMTP(close)&gt;&gt;
    278 LOG: MAIN
    278   H=mx.yandex.ru [213.180.193.89]: Remote host closed connection in response to initial connection
    278 Connecting to mx.yandex.ru [213.180.204.89]:25 ... connected
    278   SMTP(close)&gt;&gt;
    278 LOG: MAIN
    278   H=mx.yandex.ru [213.180.204.89]: Remote host closed connection in response to initial connection
    278 Connecting to mx.yandex.ru [77.88.21.89]:25 ... connected
    278   SMTP(close)&gt;&gt;
    278 LOG: MAIN
    278   H=mx.yandex.ru [77.88.21.89]: Remote host closed connection in response to initial connection
    277 LOG: MAIN
    277   == eleriya-25@yandex.ru R=dnslookup T=remote_smtp defer (-18) H=mx.yandex.ru [77.88.21.89]: Remote host closed connection in response to initial connection
  </code></pre>
  <p>Any suggestions?</p>