It’s the latest version of the 3.1 branch while the 3.3 branch contains the latest improvements and features.

Van: otrs-bounces@otrs.org [mailto:otrs-bounces@otrs.org] Namens Marwan Rabbâa
Verzonden: dinsdag 8 juli 2014 11:49
Aan: User questions and discussions about OTRS.
Onderwerp: Re: [otrs] Auto-response

Since I start my installation, the 3.1.21 was more up to date (the 3.3.8 didn't exists)