log into staff.he.net via ssh
use "mail-v":
mail-v destination_mailbox -flshort@he.net -t1
note that for it to work, 
there must be no space in "-flshort"
Example: 

lshort@staff:~$ mail-v info@promopress.com -flshort@he.net -t1
Ignoring option -1
sending email from:lshort@he.net to:info@promopress.com
Looking for MX record for promopress.com
Found promopress.com, looking up A record for it.
Done looking up address for mx record promopress.com
Found 1 ips, sorting
Done sorting
connected to 216.218.130.204
c: 220 promopress.com ESMTP Ready
s: HELO staff.he.net
c: 250 promopress.com Hello staff.he.net
s: MAIL FROM:
c: 250 lshort@he.net... Sender ok
s: RCPT TO:
c: 250 OK
s: DATA
c: 354 Start mail input; end with .
s: Message-Id: <1459707053.3184@staff.he.net.mail-v>
s: Date: Sun, 3 Apr 2016 11:10:53 -0700
s: To: info@promopress.com
s: From: lshort@he.net
s: Subject: Test Message 1
s: 
s: This is a test message.
s: It was sent at Sun, 3 Apr 2016 11:10:53 -0700

s: .
c: 250 Email accepted
s: QUIT
lshort@staff:~$