Change max recipient list size (#699)

Update max recipient list size to 6.5Mb as per ESCSP-5588 and ESCSP-5974

Author: Kieran Cooper

content/docs/user-guide/uploading-recipient-list.md

@@ -16,7 +16,7 @@ If you need an example of the format for your CSV file, select a sample to downl
 
 You may upload tags and additional information for a given recipient if required - but it is not essential. A list of correctly formatted email addresses is also acceptable. You can also edit an existing recipient list by uploading a new file to an existing label (list name).
 
-**Note:** The maximum supported size of a recipient list .csv file is **10MB**.
+**Note:** The maximum supported size of a recipient list .csv file is **6.5MB**.
 
 ## Editing an Existing Recipient List