It seems there are changes at hotmail wrt to emails sent from our ecommerce site.
One of my regular customers who has a hotmail.com email account did not receive their order confirmation email nor my confirmation emails from within the Actinic ecommerce windows client.

I then receive automated "Mail delivery failed" messages from hotmail.

I can reproduce the problem with my own hotmail account and also with a test site on the same host usingActinic's latest SellerDeck 2013 and PC client, so it is not the customers specific hotmail account causing the problem. I suspect something has changed at hotmail, maybe to do with the outlook/hotmail/live merger etc.

I can send the same message from the same SMTP server at my web host via webmail or a pop3 client to the same hotmail accounts with no problem. So its not a problem with IP blacklisting etc.

So it seem hotmail suddenly doesn't now like the way the Actinic site's scripts put the email message together.

None of my Actinic settings have changed and customers not on hotmail are fine.

The detailed rejection is:
Envelope-to: *** Email address is removed for privacy ***
Date: Wed, 11 Sep 2013 11:36:07 +0000
X-Failed-Recipients: *** Email address is removed for privacy ***
Auto-Submitted: auto-replied
From: Mail Delivery System <*** Email address is removed for privacy ***>
To: *** Email address is removed for privacy ***
Subject: Mail delivery failed: returning message to sender


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:


*** Email address is removed for privacy ***
SMTP error from remote mail server after end of data:
host mx3.hotmail.com [65.54.188.126]: 550 5.7.0 (BAY0-MC4-F38) Message could not be delivered. Please ensure the message is RFC 5322 compliant.


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


The cpanel email trace for a leter test shows:

Delivery Event Details
Event:success
User:******** removed for security
Domain:clearsystems.co.uk
Sender:*** Email address is removed for privacy ***
Sent Time:Sep 11, 2013 3:17:15 PM
Sender Host:shcp04.hosting.zen.net.uk
Sender IP:82.71.204.28
Authentication:dovecot_login
Spam Score:
Recipient:*** Email address is removed for privacy ***
Delivery User:-remote-
Delivery Domain:
Delivered To:*** Email address is removed for privacy ***
Router:lookuphost
Transport:remote_smtp
Out Time:Sep 11, 2013 3:17:15 PM
ID:1VJlEc-0006WA-E1
Delivery Host:cpanelsmarthost.zen.co.uk
Delivery IP:82.71.204.227
Size:5.13 KB
Result:Message accepted