Another easy way to find sendmail without recursively searching directories etc. is

$path = `which sendmail`;
# Perhaps check the return value here
chomp $path;

This is assuming that you are dealing in a *nixy environment.

And as far as installing an application, well, again, if you're in a *nixy environment, there is no better installer for Perl stuff than the CPAN module.

If you put something like

WriteMakefile(
    # . . . blah blah blah . . .
    'PREREQ_PM' => {
      # your dependencies go here ... the CPAN
      # module will add them to the build list
            },
    'PM' => {
      'bin/myscript' => '$(INST_SCRIPT)/myscript.pl'
            },
    # . . . blah blah blah . . .
);

in your Makefile.PL, the script will generally be placed in /usr/bin. Installing with the CPAN module would also obviate your need to check dependencies and make updating a breeze. And you can do all sorts of other wacky things from Makefile.PL, such as prompting the user for input and building a configuration file.

I'm not an expert on the CPAN module, so I don't know how exactly you'd tell it to install such-and-such a tarball in such-and-such a directory (i.e., bypassing the 'get' step and eliminating the need to have people put the tarball in, for example, /root/.cpan/build).

So, as you can see, there would be some things to think about. Just throwin' the idea out there ...

Hope this helps :-)