Ooops - how could that one have been missed... It's one of my favourite mistakes as well - Perl treats the "\" character as a special character for creating stuff like \n (newline) and \t (tab). To create an actual "\" in a string, you have to use "\\". So the correct statement would be :

  $mailprog='d:\WEBSVR\blat\blat.exe';
  warn "Couldnīt locate the mail program at $mailprog\n" unless -x $ma
+ilprog;
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Update : chromatic told me that single quotes don't interpret the backslash - and he is right. My shell (bash played the nasty trick of interpretation on me, which is even more a symptom of my difficulties with backslash interpretation ;)