For customers looking to bring down their storage, MantisHub has a plugin available to list closed issues with large attachments.
Simply install the 'Trim Attachments' plugin by going to 'Manage' - 'Manage Plugins'. You'll see it listed in the Available Plugins. Click Install.
To run the report, go to 'Manage' - 'Manage Plugins' and click on the 'Trim Attachments' Plugin
The plugin will provide a list of closed issues that have attachments sorted by issues with largest attachments at the top. You can then click on the issues and delete the attachments.
And that's it! Now you can go smell the flowers :).