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/usr/bin/test_1.sh

@@ -0,0 +1,49 @@
+#!/usr/bin/bash
+
+echo "test message" | sendmail -t root@example.com
+sleep 1
+
+## simple test if mail passes
+if [ -f /var/mail/root ] ; then
+  echo "success"
+  rm /var/mail/root
+else
+  echo "failure"
+  exit 1
+fi
+
+## test encryption
+## bob@example.com has an authenticated certificate in 
+## the cert store
+echo "test message" | sendmail -t bob@example.com
+sleep 1
+if [ -f /var/mail/bob ] ; then
+  if grep -q "BEGIN PGP MESSAGE" /var/mail/bob ; then
+    echo "encryption test: success"
+  else
+    echo "encryption test: failure"
+    exit 1
+  fi
+else
+  echo "failure: mail didn't pass"
+  exit 1
+fi
+
+## test encryption 2
+## alice@example.com has a certificate in the cert store, but
+## it is not authenticated -> this should fail
+echo "test message" | sendmail -t alice@example.com
+sleep 1
+if [ -f /var/mail/alice ] ; then
+  if grep -q "BEGIN PGP MESSAGE" /var/mail/alice ; then
+    echo "encryption test 2: failure"
+    exit 1
+  else
+    echo "encryption test 2: success"
+  fi
+else
+  echo "failure: mail didn't pass"
+  exit 1
+fi
+
+