Originally Posted by Hans
I know it is possible to select the option "Extern Mailserver" in the ISP-site module within ISPConfig.
But i do not understand how this works.. Is it not necessary to specifify an new IP-address of the External mailserver?
The "External Mailserver" option in ISPConfig prevents ISPConfig to write email addresses for that domain into the Postfix configuration, which means Postfix will not accept emails for that email addresses anymore. If Postfix receives an email for such an address, it will relay the mail to the mail server that is specified in the MX record of that domain - which means you must have an appropriate MX record for the domain.