Autoresponders are only send once to a email address, so if you test it more then once, you wont get a answer for your test emails.
When I add a user, there's the autoresponder option under 'advanced settings'. After saving I can only see 'forward' and 'Email Alias'. No longer the autoresponder option. Login as mailuser, the autoresponder settings are still there, but is not working.
Thats strange, I never seen that. Which ISPConfig version do you use?