A new option was introduced to allow users to Keep Email Attachments or have them removed automatically. This is controlled under Admin / Manage Email Defaults
The benefit of keeping the Email Attachments is that if a message is added under the Edit Text button this can be recalled and viewed.
Keeping the attachments allows for a quick re-send of an email directly from the Email Queue without having to generate it again.
But this comes at a cost, it also means the size of backups will increase overtime so will the time it takes to complete the backup.
Turning off the 'Keep Attachments' option will purge all the attachments from already sent emails reducing the time of creation and size of backups. Emails can be generated again in the software, which will create a new attachment to send.
Please see Backup Size Increasing to Purge emails on a regular basis