The Message column displays the Subject entered within the email that has been/is being sent. 

From the Sent/Cancelled tab where the Message column is empty for a message, click on the Message column for that message and a View sent message dialog will appear. 

Where a Subject has not been included the Subject field will show ‘No subject’. 

From the Pending tab, where the Message column is empty for a message, select the row and click Edit to check the Subject field. 

For more information on Communications Centre, please see KB3199 Communications Centre: Collateral.