Hello, there is an ispconfig updated to last version. Is working for more than a year with no problem with hundreds of domains. Suddenly one mailbox from one domain is not working. Is dovecot and postfix, and when is send it to the troubled mailbox (named here email@example.com) I am getting the response: This is the mail system at host mail.domain.net. I'm sorry to have to inform you that your message could not be delivered to one or more recipients. It's attached below. For further assistance, please send mail to postmaster. If you do so, please include this problem report. You can delete your own text from the attached returned message. The mail system <firstname.lastname@example.org> (expanded from <email@example.com>): mail for mail.domain.net loops back to myself I must mention that if I log on this mailbox I can send from it, but it can’t receive any mail suddenly, worked fine for a while. I’ve searched over the internet and in main.cf I have mydestination = localhost, localhost.localdomain, so this is not the solving. More.. I can create any other email address who works, but this office is not working whatever I do. I’m out of ideas, anyone can help please?