by Wendell Jones.
Hi,
I think that Josu is referring to the address that his Moodle uses in the From: for e-mails that are sent out. If that's the case, that is the No-reply address set in Administration > Site administration > Plugins > Message outputs > Email.
As an aside, our site was using this No-reply address until recently when it suddenly started using the Main administrator's address instead. This was about the time that we upgraded from 2.5+ to 2.6+, but I can't say for sure that was exactly when it changed.