Autorespond for all incoming mails/catchall/domain alias

==== Required information ====
- iRedMail version: iRedAdmin-Pro 1.5.1/iRedMail 0.8.3
- Store mail accounts in which backend (LDAP/MySQL/PGSQL):  MYSQL
- Linux/BSD distribution name and version: CENTOS 6.3
- Related log if you're reporting an issue:
====

Hello people,

do not ask why, but I need an autoresponder for a catch-all address.

I have two domains:
domain2.com is a domain alias of domain1.com
There are a info@domain1.com account configured to a catch-all incoming mails.

Now, on any mail that goes to one of the two domains it should be answered automatically with a standard text.
How can I do this best?

Thanks in advance!