In the Groups Web Interface, the Search Parameters sidebar of the Search tab has a drop-down list from which you can select a Quarantine search. One of the quarantine search options allows you to select a reason that the message was quarantined from the Reason drop-down list.
Global administrators can also add custom reasons to the default set of reasons using the pmx-group command. For example, a global administrator may want to add the reason "Offensive" so that group administrators have the option of searching for messages that were quarantined because they contain offensive language. Once enabled, a custom reason access right can be turned on or off in the same manner as other access rights.
See the pmx-group man page (man pmx-group) for more information.