You may find that MIME::Lite or one of the other email managing modules generates fewer surprises than using system commands to do the work. Consider:

# Create the message
$msg = MIME::Lite->new(
             From    =>'me@myhost.com',
             To      => $address,
             Subject => $subject,
             Type    => 'multipart/mixed'
             );

# Add the text message part:
$msg->attach(Type     =>'TEXT',
             Data     =>"Here's the GIF file you wanted"
             );

# Add the file part:
$msg->attach(Type     =>'TEXT',
             Path => $filename,
             Disposition => 'attachment'
             );

$msg->send ();
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