We are using Customer-Specific SPAM Submissions from a long time and administrators submit samples using control center. As per Symantec, these submissions only work if those are submitted within 24 hours of receipt. Most of the times it does not happen that way as users take more than 24 hrs time to report 'Missed SPAMs' to security team. Hence those submissions do not result in signature creation.
Moreover, Symantec does not support integration with email systems other than microsoft exchange, by which users could submit the mails at their own (Self Service).
We would like to suggest Symantec, to provide a functionality so that the users could upload the samples to their spam quarantine login and those samples get automatically submitted to Symantec.
We would like to request other community members to vote for it as it'll be very useful feature for all of us. And Symantec must consider for a future release.