I'm not quite sure why you need to use Net::SMTP in your example, I've had luck with code like the following:

use strict; use warnings;
use MIME::Lite;
        
my $msg = MIME::Lite->build(
    From    => 'from@mail.address',
    To      => 'recipient@mail.address',
    Subject => 'some subject',
    Type    => 'multipart/mixed',
);  
                  
$msg->attach( Type     => 'TEXT',
              Data     => "see attached file\n\n"
            );
    
                  
$msg->attach( Type => 'AUTO',  # change AUTO to your prefered type if 
+you wish
              Path => '/path/to/some/file',
);  
                  
# MIME::Lite->send('smtp', 'some.smtp.host' );  # don't use sendmail, 
+see POD

$msg->send();
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