I have found a problem with SG. Some servers (such as Gmail) do not allow some kind of attachments (.exes, .zip with .exes inside).
If you try to send a message to a Gmail account with an .exe attachment, you get this message. (I did it from a yahoo address)
Date: 20 Jun 2004 19:33:50 -0000
Subject: failure delivery
Message from yahoo.com.
Unable to deliver message to the following address(es).
22.214.171.124 failed after I sent the message.
Remote host said: 552 Illegal Attachment
--- Original message follows.
The original message is over 5k. Message truncated to 1K.
Received: from [126.96.36.199] by web25307.mail.ukl.yahoo.com via HTTP;
Sun, 20 Jun 2004 12:33:47 PDT
Date: Sun, 20 Jun 2004 12:33:47 -0700 (PDT)
From: RS <email@example.com>
Subject: exe file
Content-Type: text/plain; charset=us-ascii
So, if you send a message to a SG account that poins to Gmail, nobody notices anything wrong, SG counter of redirected messages increases one, but the recipient never gets the message.
Is there a way of noticing the sender that his message didn't arrive without causing much trouble to the SG server?