E-mail FAILED

[محروم.كوم]

One of my moderators was saying that she didn't always get her notifications of new threads, so I checked her settings to confirm that they were correct, but I also enabled the e-mail logging to check and see whether the notifications were going out or not.

I haven't quite determined the cause of the lack of notifications, but in the log, I see "FAILED" before an e-mail to her. How do I determine the cause of the failure?

Here's the part of the log, 2 moderators were notified, her and myself (andy), and mine went through fine. (her e-mail address is valid, and yes, the message was from a spammer who I've subsequently banned)
Quote:
================================================== ===
FAILED
Mon, 30 Aug 2010 22:44:51 -0400
To: [email protected]
Subject: New Post/Thread Notification: General
From: "xxx Forums" <a href="mailto:[email protected]"[email protected]/a>
Return-Path: [email protected]
Auto-Submitted: auto-generated
Message-ID: <a href="mailto:[email protected] "[email protected]/a>
MIME-Version: 1.0
Content-Type: text/plain; charset="ISO-8859-1"
Content-Transfer-Encoding: 8bit
X-Priority: 3
X-Mailer: vBulletin Mail via PHP

Hello,
yyy has just posted in the General forum of xxx Forums under the title of Don't you have a thought to buy cheap things?.
This thread is located at http://www.xxx.com/forum/showthread.php?t=1191
Here is the message that has just been posted:
***************
It's sure that air max nike shoes are especially popular in this year
***************
================================================== ===
SUCCESS
Mon, 30 Aug 2010 22:44:51 -0400
To: [email protected]
Subject: New Post/Thread Notification: General
From: "xxx Forums" <a href="mailto:[email protected]"[email protected]/a>
Return-Path: [email protected]
Auto-Submitted: auto-generated
Message-ID: <a href="mailto:[email protected] "[email protected]/a>
MIME-Version: 1.0
Content-Type: text/plain; charset="ISO-8859-1"
Content-Transfer-Encoding: 8bit
X-Priority: 3

X-Mailer: vBulletin Mail via PHP

Hello,
yyy has just posted in the General forum of xxx Forums under the title of Don't you have a thought to buy cheap things?.
This thread is located at http://www.xxx.com/forum/showthread.php?t=1191
Here is the message that has just been posted:
***************
It's sure that air max nike shoes are especially popular in this year
***************
================================================== === __DEFINE_LIKE_SHARE__