I'm not sure why it is behaving differently if the file doesn't exist - can you show how you create the ftps object?

You can always check yourself that the file exists before calling put:

if ( ! -e $file ) {
    emailerr("$file does not exist");
}
else {
    $ftps->put($file);
}
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To check if put() was successful you only need to see if the last FTP status code starts with "2", so:

my $rtncode = $ftps->last_status_code;
if ( $rtncode != 2 ) {
    # deal with error
}
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Note: last_status_code() returns the first digit from the full 3 digit response code.