milter support

Dockerfile

@@ -47,6 +47,10 @@ ENV SMTP_TLS_MANDATORY_PROTOCOLS=""
 ENV SMTP_TLS_NOTE_STARTTLS_OFFER=""
 ENV SMTP_TLS_SECURITY_LEVEL=""
 ENV SMTP_TLS_SESSION_CACHE_DATABASE=""
+ENV SMTPD_MILTERS=""
+ENV NON_SMTPD_MILTERS="\$smtpd_milters"
+ENV MILTER_DEFAULT_ACTION=accept
+ENV INTERNAL_MAIL_FILTER_CLASSES=bounce
 
 # TODO: template access lists