Hello everyone, probably a silly question, but I can't imagine the solution. I followed the perfect Debian-Apache guide. I configured isp with an A field > srv-b.MasterDomain.com = ok! I left the DNS management at my registrar > my ispConfig and I only enter the DNS zone per domain to redirect to Code: srv-b.MasterDomain.com Then I configured 2 other domains I need in ispConfig + email accounts. = OK Example: [email protected] I'm trying to understand that I have to enter the information in my local mail client "ThunderBird" as smtp host. I was thinking that logically, I should indicate in smtp my main domain : Code: srv-b.MasterDomain.com for outgoing mails. But this must be a mistake, because for each account configured in Tunderbird, I am asked for a login and password per email account. Do I have to create as many smtp+login+password smtp infos in Thunderbird as I have e-mail accounts, or is it possible in the Postfix configuration file to tell it that there is only one main mail address for all my domains Code: mails.MasterDomain.com as A entry and tell it which ones. Thanks to you.