The remote email client may attach unrequested attachments to an outgoing email.
The remote host is running eGroupWare, a web-based groupware solution. It is reported that versions prior 1.0.0.007 are prone to an information disclosure vulnerability. Specifically, if a user composes an email with an attachment and then cancels the email, the attachment will be attached and sent with the next outbound email.
Upgrade to eGroupWare 1.0.0.007 or higher.