Mailer Daemon

I am unable to send out email to certain people without getting these errors. I am running MWB right now. Please let me know what to do. I am unable to email customers.... thanks in advance.
Delivery to the following recipient failed permanently:

<snip>


Technical details of permanent failure:
Google tried to deliver your message, but it was rejected by the recipient domain. We recommend contacting the other email provider for further information about the cause of this error. The error that the other server returned was: 550 550-5.1.1 The email account that you tried to reach does not exist. Please try
550-5.1.1 double-checking the recipient's email address for typos or
550-5.1.1 unnecessary spaces. Learn more at
550 5.1.1 http://support.google.com/mail/bin/answer.py?answer=6596 r58si199877weq.43 (state 14).

----- Original message -----

MIME-Version: 1.0
Received: by 10.216.134.160 with SMTP id s32mr11196550wei.36.1328732381792;
Wed, 08 Feb 2012 12:19:41 -0800 (PST)
Received: by 10.223.58.13 with HTTP; Wed, 8 Feb 2012 12:19:41 -0800 (PST)
Date: Wed, 8 Feb 2012 13:19:41 -0700
Message-ID: <CALi3RZPhXp8T98+=K34To4G6Z0ykWgwzUET5P0tdHQOF906yTA@mail.gmail.com>
Subject:
From: <snip>
To:<snip>
Content-Type: multipart/alternative; boundary=0016e6de00ec9e499104b8799d2a

and

Delivery to the following recipient failed permanently:

<snip>

Technical details of permanent failure:
Google tried to deliver your message, but it was rejected by the recipient domain. We recommend contacting the other email provider for further information about the cause of this error. The error that the other server returned was: 554 554 delivery error: dd This user doesn't have a yahoo.com account (<snip>) [0] - mta1055.mail.ac4.yahoo.com (state 18).

----- Original message -----

Received: by 10.50.203.98 with SMTP id kp2mr34809559igc.5.1328716891827;
Wed, 08 Feb 2012 08:01:31 -0800 (PST)
Return-Path: <snip>
Received: from (67-61-33-230.cpe.cableone.net. [67.61.33.230])
by mx.google.com with ESMTPS id or2sm485525igc.5.2012.02.08.08.01.29
(version=SSLv3 cipher=OTHER);
Wed, 08 Feb 2012 08:01:30 -0800 (PST)
Message-ID: <3E65CC347FA8489C9102A1B7FDD72D55@SNOWPC>
From: <snip>
To: <snip>
Subject: case #35448
Date: Wed, 8 Feb 2012 09:01:43 -0700
Organization: MUFON International
MIME-Version: 1.0
Content-Type: multipart/related;
type="multipart/alternative";
boundary="----=_NextPart_000_0194_01CCE640.47018880"
X-Priority: 1
X-MSMail-Priority: High
X-Mailer: Microsoft Windows Mail 6.0.6002.18197
X-MimeOLE: Produced By Microsoft MimeOLE V6.0.6002.18463