Note that the File::Find method may not be overly secure if used in a simplistic way. People with any kind of write access can happily drop any program into their space and call it 'Sendmail', and if you're just relying on the filename (or even on it acting vaguely like Sendmail.. it's not overly tricky to do a basic impersonation to hide evilcode) then you're going to end up calling unknown and untrusted code.

Even without this it's possible that you'd end up calling an old version kept around for compatibility reasons or so on.

Possibly the best way to handle this, in my opinion, would be to ask the user installing the script which version of Sendmail to use and offering /usr/bin/sendmail as a default if it exists.