# echo "Hello world" | swaks -4 --server localhost:25 --from alex.hha@gmail.com --to alex@example.net --h-Subject "Test message" --body -
=== Trying localhost:25...
=== Connected to localhost.
<-  220 smtp.example.net ESMTP Postfix
 -> EHLO jenkins.example.net
<-  250-smtp.example.net
<-  250-PIPELINING
<-  250-SIZE 10240000
<-  250-VRFY
<-  250-ETRN
<-  250-ENHANCEDSTATUSCODES
<-  250-8BITMIME
<-  250 DSN
 -> MAIL FROM:<alex.hha@gmail.com>
<-  250 2.1.0 Ok
 -> RCPT TO:<alex@example.net>
<-  250 2.1.5 Ok
 -> DATA
<-  354 End data with <CR><LF>.<CR><LF>
 -> Date: Tue, 15 Mar 2016 09:34:18 +0000
 -> To: alex@example.net
 -> From: alex.hha@gmail.com
 -> Subject: Test message
 -> X-Mailer: swaks v20130209.0 jetmore.org/john/code/swaks/
 ->
 -> Hello world
 ->
 ->
 -> .
<-  250 2.0.0 Ok: queued as 8F6CE1C0B33
 -> QUIT
<-  221 2.0.0 Bye
=== Connection closed with remote host.

# grep 8F6CE1C0B33 /var/log/maillog
Mar 15 09:34:18 ci postfix/smtpd[24556]: 8F6CE1C0B33: client=localhost[127.0.0.1]
Mar 15 09:34:18 ci postfix/cleanup[24559]: 8F6CE1C0B33: message-id=<20160315093418.8F6CE1C0B33@smtp.example.net>
Mar 15 09:34:18 ci postfix/qmgr[24553]: 8F6CE1C0B33: from=<alex.hha@gmail.com>, size=428, nrcpt=1 (queue active)
Mar 15 09:34:18 ci postfix/smtp[24560]: 8F6CE1C0B33: to=<alex@example.com>, orig_to=<alex@example.net>, relay=smtp.example.com[192.168.88.230]:25, delay=0.06, delays=0.02/0.01/0.01/0.03, dsn=2.0.0, status=sent (250 2.0.0 Ok: queued as BFFDA6065D)
Mar 15 09:34:18 ci postfix/qmgr[24553]: 8F6CE1C0B33: removed

orig_to=<alex@example.net>

to=<alex@example.com>

# grep 292366065D /var/log/maillog
Mar 15 06:38:07 relay postfix/smtpd[19245]: 292366065D: client=smtp.example.net[192.168.88.87]
Mar 15 06:38:07 relay postfix/cleanup[19248]: 292366065D: message-id=<20160315093810.E71EA1C0B33@smtp.example.net>
Mar 15 06:38:07 relay postfix/qmgr[19244]: 292366065D: from=<alex.hha@gmail.com>, size=622, nrcpt=1 (queue active)
Mar 15 06:38:07 relay postfix/virtual[19249]: 292366065D: to=<alex@example.com>, relay=virtual, delay=0.03, delays=0.02/0.01/0/0, dsn=2.0.0, status=sent (delivered to maildir)
Mar 15 06:38:07 relay postfix/qmgr[19244]: 292366065D: removed

# cat /var/mail/virtual/example.com/alex
Return-Path: <alex.hha@gmail.com>
X-Original-To: alex@example.com
Delivered-To: alex@example.com
Received: from smtp.example.net (smtp.example.net [192.168.88.87])
        by smtp.example.com (Postfix) with ESMTP id 292366065D
        for <alex@example.com>; Tue, 15 Mar 2016 06:38:07 -0400 (EDT)
Received: from jenkins.example.net (localhost [127.0.0.1])
        by smtp.example.net (Postfix) with ESMTP id E71EA1C0B33
        for <alex@example.net>; Tue, 15 Mar 2016 09:38:10 +0000 (UTC)
Date: Tue, 15 Mar 2016 09:38:10 +0000
To: alex@example.net
From: alex.hha@gmail.com
Subject: Test message
X-Mailer: swaks v20130209.0 jetmore.org/john/code/swaks/
Message-Id: <20160315093810.E71EA1C0B33@smtp.example.net>

Hello world