So im not sure what you mean by more efficient. In terms of runtime, or in terms of regex construction. I also dont know what you mean by any pieces of its name, or rather how paranoid you want to be. but this is what I have.

#!/usr/bin/perl

use strict;

my $str;
my $tomatch = 'foobar the vacation.msg is here';
my @permute = map { 
   $str; $str = $_ . $str; 
} ( reverse( split(//, 'vacation') ) );

$regex = '(\.?(?:' . join('|', reverse(@permute)) . ')\.msg)';

print "$regex\n";

print "Match: $1\n" if ($regex =~ m/$tomatch/ );
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HTH

MMMMM... Chocolaty Perl Goodness.....