The way administrators perform actions on multiple emails through Mail Explorer has changed a bit.
The way administrators quarantine / restore / export a list of mail records from Mail Explorer has changed.
Now, administrators can check the "Select all" box next to the list of items to select all visible records.
Then, in order to select all the emails matching the filter, they can click on the "select all [number]" link.
Finally, the list of available actions no longer contain the "Restore all Matching" and "Quarantine all Matching" options, as they are now redundant.
Instead, after clicking on "select all [number]" link, simply select the desired action (Restore / Quarantine / Export to CSV)
Note - this feature is now being gradually deployed and will become available in your account during the next week.