Hello ctrevgo_learn_perl, and welcome to the Monastery!

As graff says, you need to supply more information. For example, what is the format of a typical line read from the file “test.txt”? There seems to be some confusion:

# Strip the mbox and id, assuming the file contains mbox:id
  my($mbox,$id)=split(',',$_);
[download]

Aside from the fact that there is no stripping happening here, the comment specifies that the initial two items will be separated by a colon, but the code assumes a comma. If the comment is correct but the data line happens to contain a comma somewhere, this will “work” without warnings but will produce spurious results.

I note also that the script has:

use File::Slurp qw(read_dir);
...
use Data::Dumper;
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but neither module appears to be actually used?

And an observation on style. The use constant declarations can be written more clearly, like this:

use constant
{
    DRY          => 1,                   # Dry run. 0 will execute
    FILE         => 'test.txt',          # Hardcoding the file path as
+ of now
    STATS_FILE   => 'mbox_stats.txt',    # Successful operation - stat
+s file
    MBOX_UNKNOWN => 'mbox_unknown.txt',  # Failed mailbox operations
    VOL          => '/home/folder/',     # TOP Level volume directory
    DEBUG        => 1,
};
[download]

Hope that helps,