To restore email marked as spam by amavis we going to use the command amavisd-release

First edit the amavisd-release script to ensure that $socketname is properly configured, got to be something like this:

 $socketname = '/var/vscan/amavisd.sock';

next check the log file for the serial of the mail, eg:

mavis[29297]: (29297-01-6) Blocked SPAM, ... <...> -> <...>,
  quarantine: spam/U/UM3XM3XDbN52.gz,
              ^^^^^^^^^^^^^^^^^^^^^^
  Message-ID:<...>, mail_id: UM3XM3XDbN52, Hits: 13.365,

and to recover that specific message run the command:

 amavisd-release spam-UM3XM3XDbN52.gz mail@example.com

where mail@example.com is the recipient address that will receive the recovered email