Outlook Express emails go missing

I am on TalkTalk broadband and I am having intermittant trouble with emails sent to and from Outlook Express (6 I think) going missing.
The word intermittant is important because some days everything works perfectly and other days like now it is not.
Currently when I send an email to myself it does not arrive when previously it comes in very quickly.
Strangely if I go onto TalkTalk webmail and send an email to myself, it arrives on Outlook Express.
Similarly a lot of emails I send to other people from OE don't arrive at their destination and other people have had trouble sending me emails.
Somebody has just sent me a non-delivery email they received when trying to send to me which I will try to paste on the end here.
I have spent hours on the phone to TalkTalk who checked all my email settings were correct. In the end they said it was nothing to do with TalkTalk and there must be a software glitch in Outlook Express.
What I don't understand if it is NOT something to do with TalkTalk is why some days it should work, and other days not. If there is a software prob with OE, wouldn't it always be faulty?
I know I've been here before but I need some help please...
Below is a failure notice somebody sent me:
I will delete the actual email addresses...
Thanks

----- Original Message -----
From: <>
To: <>
Sent: Sunday, June 15, 2008 9:57 PM
Subject: failure notice


> Sorry, we were unable to deliver your message to the following address.
>
> <>:
> Mail server for "talkalk.net" unreachable for too long
>
> --- Below this line is a copy of the message.
>
> Received: from [217.146.182.178] by n22.bullet.mail.ukl.yahoo.com with
> NNFMP; 13 Jun 2008 20:50:56 -0000
> Received: from [217.146.182.191] by t4.bullet.ukl.yahoo.com with NNFMP; 13
> Jun 2008 20:50:56 -0000
> Received: from [127.0.0.1] by omp105.mail.ukl.yahoo.com with NNFMP; 13 Jun
> 2008 20:50:56 -0000
> X-Yahoo-Newman-Property: ymail-5
> X-Yahoo-Newman-Id:
> Received: (qmail 28486 invoked by uid 60001); 11 Jun 2008 13:12:00 -0000
> DomainKey-Signature: a=rsa-sha1; q=dns; c=nofws;
> s=s1024; d=btinternet.com;
>
> h=Received:X-Mailerate:From:Subject:To:MIME-Version:Content-Type:Message-ID;
>
> b=R5gb9CAolNExW6li5eufmOs/pm4YnhVnQo3lNg0SH3VG3XNM65QLjDYtabXSHM1PbT8mU7EmN6 J4sSzu4js9ER9C/fG+gFhVucvcIN4ZCfFGw1TEZ6ZkHf2EIwgBLSiCkIvJSxxUFbE TMJ516JjSDnPg1uBd8mzSg43SnjkMQXg=;
> Received: from [83.104.205.170] by web86613.mail.ird.yahoo.com via HTTP;
> Wed, 11 Jun 2008 13:11:59 GMT
> X-Mailer: YahooMailRC/975.41 YahooMailWebService/0.7.185
> Date: Wed, 11 Jun 2008 13:11:59 +0000 (GMT)
> From: Phil
> Subject: Tulpa or Tulku?
> To: Dave <>,> MIME-Version: 1.0
> Content-Type: multipart/alternative;
> boundary="0-1695682674-1213189919=:24988"
> Message-ID: <>
>
> --0-1695682674-1213189919=:24988
> Content-Type: text/plain; charset=utf-8
> Content-Transfer-Encoding: quoted-printable
>