Activity Generated in CRM through an incoming Email

Hi,

Im new to CRM.Can anyone one help me in this issue.

When an User sends a Email with HTML attachment to CRM System, an Activity is generated at CRM end.

But when i try opening the Attachment in the Activity,it doesn't open.It works fine for Word Document and PDF attachments.

Can anyone suggest me how this activity is generated when an email comes.Any processing steps or Configuration to be done.Need to know whether HTML format is Supported?????

Thanks,

Anuja