Ask your friend to tell you word for word what the bounce message says. Bounces always contain the exact, precise reason that the email bounced, but the reason why is surrounded by a bunch of numbers, so the person who gets the bounce may be intimidated and frightened by what looks like computer code and may not read the message.
Here are two sample bounce messages. I have put in bold the part that explains why the message bounced.
----------------------
From: Mail Delivery Subsystem <MAILER-DAEMON@abbmta1.siu.edu>
Date: October 25, 2006 1:43:48 PM CDT
To: calion@mac.com
Subject: Returned mail: see transcript for details
The original message was received at Tue, 24 Oct 2006 11:13:10 -0500 (CDT)
from 12-207-137-62.client.mchsi.com [12.207.137.62]
----- The following addresses had permanent fatal errors -----
<support@symtoys.com>
(reason: 451 timeout (#4.4.2))
----- Transcript of session follows -----
... while talking to smtp.secureserver.net.:
DATA
<<< 451 timeout (#4.4.2)
... while talking to mailstore1.secureserver.net.:
DATA
<<< 451 timeout (#4.4.2)
<support@symtoys.com>... Deferred: 451 timeout (#4.4.2)
Message could not be delivered for 1 day
Message will be deleted from queue
----------------------
The original message was received at Fri, 20 Oct 2006 17:50:50 -0400 (EDT)
from 62-192.124-70.tampabay.res.rr.com [70.124.192.62]
----- The following addresses had permanent fatal errors -----
<piracy@microsoft.com>
(reason: 550 5.7.1 <Your e-mail was rejected by an anti-spam content filter on gateway (IP_Address).Reasons for rejection may be: obscene language, graphics, or spam-like characteristics. Removing these may let the e-mail through the filter.>)
----- Transcript of session follows -----
... while talking to maila.microsoft.com.:
DATA
<<< 550 5.7.1 <Your e-mail was rejected by an anti-spam content filter on gateway (IP_Address).Reasons for rejection may be: obscene language, graphics, or spam-like characteristics. Removing these may let the e-mail through the filter.>
554 5.0.0 Service unavailable
Reporting-MTA: dns; ms-smtp-03.tampabay.rr.com
Received-From-MTA: DNS; 62-192.124-70.tampabay.res.rr.com
Arrival-Date: Fri, 20 Oct 2006 17:50:50 -0400 (EDT)