Incoming emails are not in the right place

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?

 

The lineup is as follows:

The main email server that forwards the emails of certain users to us is mail.valami.hu and is in a completely different network, locally elsewhere.
The name of our server is isp.valami.hu, but we receive the mail at mx2.valami.hu.

Our server hosts file:

127.0.0.1 localhost
172.16.1.16 valami.prx.local something (this is an internal proxmox network)
external ip isp.valami.hu isp mx2.valami.hu mx2

The "essential" content of main.cf is:

myhostname = isp.valami.hu
myorigin = isp.valami.hu
mydestination = mx2.valami.hu, localhost, localhost.localdomain
relayhost =
mynetworks = 127.0.0.0/8 [:: 1] / 128
inet_interfaces = all
inet_protocols = all
virtual_mailbox_base = /var/vmail

In the log I noticed that it differs in 2 lines:

When an mx record points to the server, so we receive the mail directly, the following appears:

Apr 21 14:26:05 isp postfix / lmtp [158380]: 6527D101CA0: to = <[email protected]>, relay = 127.0.0.1 [127.0.0.1]: 10024, delay = 0.55, delays = 0.26 / 0.01 / 0.01 / 0.27, dsn = 2.0.0, status = sent (250 2.0.0 from MTA (smtp: [127.0.0.1]: 10025): 250 2.0.0 Ok: queued as 948EF101CA1)
Apr 21 14:26:05 isp postfix / qmgr [3726755]: 6527D101CA0: removed
Apr 21 14:26:05 isp dovecot: lmtp ([email protected]) <158386> <[email protected]>, relay = isp.valami.hu [private / dovecot-lmtp], delay = 0.28, delays = 0.08 / 0.01 / 0.01 / 0.18, dsn = 2.0.0, status = sent (250 2.0.0 <[email protected]> jbHqKV1NYWKyagIAbwWYLQ Saved)

When they are forwarded to us, this will include:

Apr 22 09:11:47 isp postfix / lmtp [211790]: 21BE2C40DCB: to = <[email protected]>, relay = 127.0.0.1 [127.0.0.1]: 10026, delay = 4.1, delays = 0.2 / 0.01 / 0 / 3.8, dsn = 2.0.0, status = sent (250 2.0.0 from MTA (smtp: [127.0.0.1]: 10027): 250 2.0.0 Reason: queued as 1B1F1C40DD2)
Apr 22 09:11:47 isp postfix / qmgr [211782]: 21BE2C40DCB: removed
Apr 22 09:11:47 isp postfix / local [211794]: 1B1F1C40DD2: to = <[email protected]>, relay = local, delay = 0.11, delays = 0.05 / 0.01 / 0 / 0.05, dsn = 2.0 .0, status = sent (delivered to mailbox)

It can be seen that if it is forwarded to us, it does not come as [email protected], but as [email protected], and then it does not process dovecat, but postfix, and so at realy local is listed and not the server name.

 

SOLVED: add mx2.valami.hu on Domain ear, and make domain alias to telemedia.hu. Then create new mailbox, and working like a charm.