Start milestone 3

- Add functionality to query online sources (Keyservers, etc) for
  certificates.
- Use introducers to determine which UserIDs should be fetched from
  online soources. Check certifications before importing certifiactes
  into the local cert store.
- start docker image for local end-to-end testing.

docker/mta_provision/etc/postfix/main.cf

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+#
+# minimal postfix configuration with enabled milter
+#
+
+# 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 = $myhostname ESMTP $mail_name (Debian/GNU)
+biff = no
+
+# appending .domain is the MUA's job.
+append_dot_mydomain = no
+
+# Uncomment the next line to generate "delayed mail" warnings
+#delay_warning_time = 4h
+
+#readme_directory = /usr/share/doc/postfix
+
+# See http://www.postfix.org/COMPATIBILITY_README.html -- default to 3.6 on
+# fresh installs.
+compatibility_level = 3.6
+
+# Per Debian policy, default to /etc/postfix for Cyrus SASL config
+cyrus_sasl_config_path = /etc/postfix/sasl
+
+
+# TLS parameters
+smtpd_tls_cert_file=/etc/ssl/certs/ssl-cert-snakeoil.pem
+smtpd_tls_key_file=/etc/ssl/private/ssl-cert-snakeoil.key
+smtpd_tls_security_level=may
+
+smtp_tls_CApath=/etc/ssl/certs
+smtp_tls_security_level=may
+smtp_tls_session_cache_database = btree:${data_directory}/smtp_scache
+
+
+smtpd_relay_restrictions = permit_mynetworks permit_sasl_authenticated defer_unauth_destination
+myhostname = example.com
+myorigin = example.com
+alias_maps = hash:/etc/aliases
+alias_database = hash:/etc/aliases
+mydestination = $myhostname, localhost.localdomain, localhost
+#relayhost = 
+mynetworks = 127.0.0.0/8 [::ffff:127.0.0.0]/104 [::1]/128 192.168.1.0/24
+mailbox_size_limit = 0
+recipient_delimiter = +
+inet_interfaces = all
+inet_protocols = all
+
+smtpd_milters = inet:localhost:3000
+non_smtpd_milters = $smtpd_milters

docker/mta_provision/etc/sudoers.d/user_sudo

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+user	ALL=(ALL) NOPASSWD:ALL