postfix: accept whole mail before passing it to filtermail

upstream: chatmail/relay#673

Author: feld

templates/default/master.cf.erb

@@ -31,6 +31,7 @@ submission inet n       -       y       -       5000    smtpd
   -o smtpd_relay_restrictions=permit_sasl_authenticated,reject
   -o milter_macro_daemon_name=ORIGINATING
   -o smtpd_client_connection_count_limit=1000
+  -o smtpd_proxy_options=speed_adjust
   -o smtpd_proxy_filter=127.0.0.1:10080
 smtps     inet  n       -       y       -       5000    smtpd
   -o syslog_name=postfix/smtps
@@ -48,6 +49,7 @@ smtps     inet  n       -       y       -       5000    smtpd
   -o smtpd_relay_restrictions=permit_sasl_authenticated,reject
   -o smtpd_client_connection_count_limit=1000
   -o milter_macro_daemon_name=ORIGINATING
+  -o smtpd_proxy_options=speed_adjust
   -o smtpd_proxy_filter=127.0.0.1:10080
 #628       inet  n       -       y       -       -       qmqpd
 pickup    unix  n       -       y       60      1       pickup