IMAP email attachement sending issues

We are experiencing difficulty sending emails that include logo's and attachments that are produced by our case management system.

We use Outlook 2003 and produce emails from our case management system. We use IMAP email accounts provided by uk2.net. The emails send fine to clients that use MS Outlook, however programs such as Windows Live remove the attachments with no notification. The attachments are present when the user logs into the web interface but not when using client programs or iphones etc.

The issue only seems to occur when emails are generated from our case management system. They are delivered correctly when a user creates the mail directly through outlook & manually attaches an attachment.

I have read various suggestions that the issue relates to the mail type i.e. RFT or HTML. I have set everything possible to HTML (unless I’ve missed anything).

It seems strange that the issue only relates to mail sent from our case management system. It also removes any logo's that are embedded in the email.

I’m happy for somebody to look at the issue on site or remotely.