Hello, |tr a-zA-Z n-za-mN-ZA-M| does not work under Windows 7. http://www.claws-mail.org/faq/index.php/Actions says: This will apply the rot13 cyphering algorithm to the (selected) text in the message/compose view. Don't work under Windows 7. I use Claws Mail for Usenet. Please fix it.
Thanks for reporting, Actions page fixed now.