SYMPTOM
In Strategy Intelligence Server 9.x, email subscriptions are not delivered with the error "Message contains invalid header".
Although the subscription is created successfully, Distribution Services administrator receives the “undelivered mail returned to sender” notification. The notification includes the error that message contains an invalid header, as shown below:

CAUSE
On the mail server side, the server rejects the email because the message-ID is empty. Strategy Distribution Services 9.x leaves the Message-ID field empty as per the current working design.
The Attachment Content Code is not in the proper format and the mailbox server rejects the mail with this error code "said: 554 5.6.0 Message contains invalid header (in reply to end of DATA command)|0| ". This is because thee mail has an empty Message-ID as shown below:
From: "aaa" < xxx@yyy.com >>Reply-To: "aaa" < xxx@yyy.com >>To: " xxx@yyy.com " < xxx@yyy.com >>Date: Fri, 9 May 2014 18:12:39 +0530Subject: DailyDisbursalExcelImportance: normalMessage-ID:X-MailServ-MailFilter-MailScanner-Information: Please contact the ISP for more informationX-MailServ-MailFilter-MailScanner-ID: 03E7B5FBDF.AA10DX-MailServ-MailFilter-MailScanner: Found to be cleanX-MailScanner-From: xxx@yyy.com

Refer to the following Strategy Knowledge Base document below to perform steps to manually deliver an email:
KB11482 -- How to deliver an e-mail manually for SMTP troubleshooting purposes?
ACTION
An enhancement request has been logged to have a Message-ID populated in the email header. Contact Strategy Technical Support for an update regarding this issue.
For the email delivery to go through, the mail server settings have to be modified so that emails with empty Message-IDs will be accepted.