I ran into a problem installing a Debian server (11.3) with the latest ISPConfig (autoinstaller) on it, which will run a mail server (postfix + dovecot + amavis). I had already done such a test and it worked without any problems when a direct MX record pointed to the external Ip. However, the new lineup is that no MX record points to the server I create, but another server filters the mail and forwards the emails to us for certain email addresses. In this case, however, the e-mails are not created under /var/vmail in the Maildir format, but under /var/mail as 1 file with the user's name, and append the e-mails for this, even though. This problem only occurs if the mail is forwarded to our server from another email server (on which exim4 is running anyway). What could be the problem?