Under the released new design there are broken links within - https://engage6.silverpop.com/mailingsManagementTemplate.do

Sometimes, invalid links to mailing ids are generated on clickthrough from the list of mailings. The invalid link format is https://engage6.silverpop.com/msg-mgmt/mailingID (https://engage6.silverpop.com/msg-mgmet/mailingID)

This effectively disables the option to edit emails for some users, unless they know that they need to manually workaround to the old structure.