i have a friend who has an @yahoo address who i mail regularly. i'm finding that approx 1 out of every 4 e-mails i send to him regularly bounce back - but a week later - and for the entire week i have no idea he hasn't read my mail. this has been going on for months, and it's very frustrating. what can i do about it?

i'm on a lunarpages basic hosting plan. no other problems with any other e-mail. his e-mails back to me always arrive fine.

here's the headers of one sample message i tried to send him, which bounced back a week later:

This message was created automatically by mail delivery software.

A message that you sent could not be delivered to one or more of its
recipients. This is a permanent error. The following address(es) failed:

 myfriendsaddress@yahoo.com

------ This is a copy of the message, including all the headers. ------

Return-path: <me@mylunarpagesdomain.com>
Received: from localhost ([127.0.0.1])
   by gaia.lunarpages.com with esmtpa (Exim 4.68)
   (envelope-from <me@mylunarpagesdomain.com>)
   id 1JvclD-0007l4-H3; Mon, 12 May 2008 11:28:31 -0700
Received: from 12.181.80.172 ([12.181.80.172]) by mylunarpagesdomain.com (Horde MIME
   library) with HTTP; Mon, 12 May 2008 11:28:26 -0700
Message-ID: <20080512112826.s0wvsd4r204o0swk@mylunarpagesdomain.com>
Date: Mon, 12 May 2008 11:28:26 -0700
From: My Name <me@mylunarpagesdomain.com>
To: Dan <myfriendsaddress@yahoo.com>
Subject: Re: x-48
References: <733813.32715.qm@web52603.mail.re2.yahoo.com>
In-Reply-To: <733813.32715.qm@web52603.mail.re2.yahoo.com>
MIME-Version: 1.0
Content-Type: text/plain;
   charset=ISO-8859-1;
   DelSp="Yes";
   format="flowed"
Content-Disposition: inline
Content-Transfer-Encoding: quoted-printable
User-Agent: Internet Messaging Program (IMP) H3 (4.1.6)