specify mail.host and mail.from in email props

At least one of these is needed to generate a proper Message-ID header
with a valid FQDN.

Author: thestinger

src/main/java/app/attestation/server/AlertDispatcher.java

@@ -110,6 +110,7 @@ public void run() {
                         continue;
                     }
                     final Properties props = new Properties();
+                    props.put("mail.from", emailFrom);
                     props.put("mail.smtp.connectiontimeout", Integer.toString(TIMEOUT_MS));
                     props.put("mail.smtp.timeout", Integer.toString(TIMEOUT_MS));
                     props.put("mail.smtp.writetimeout", Integer.toString(TIMEOUT_MS));
@@ -121,6 +122,8 @@ public void run() {
                     }
 
                     final Properties props = new Properties();
+                    props.put("mail.host", emailHost);
+                    props.put("mail.from", emailFrom);
                     props.put("mail.transport.protocol.rfc822", "smtps");
                     props.put("mail.smtps.auth", true);
                     props.put("mail.smtps.host", emailHost);