email server problems

I am installing perfect server with roundcube & ispconfig 3.
It is very good instruction.
Much easy then other variants.
I have problem installing by your instruction on centos 7/8 and debian 9/10 or ubuntu 20.04. installing on digital ocean vps, hetzner vps, linode. Now testing on my own server. istallation going ok usualy.
But when i start mail server - add mail domain, then add mail box - mailbox is empty in incoming. outcome email is normal. and normal going to other servers.
What i am doing wrong and how to fix it?

also roundcube shows error 250 when trying to send mail.
i`ve installed on this intruction about month or two before and has no errors. do not understand what to show and what to do.

##### SERVER #####
IP-address (as per hostname): ***.***.***.***
[WARN] could not determine server's ip address by ifconfig
[INFO] OS version is Ubuntu 18.04.5 LTS

[INFO] ISPConfig is installed.

##### ISPCONFIG #####
ISPConfig version is 3.1dev

 

also
debian 10.0.6 on my server trying to install perfect server
installation errors

Code:

 dpkg-reconfigure dash
bash: dpkg-reconfigure: command not found

Code:

 a2enmod suexec rewrite ssl actions include dav_fs dav auth_digest cgi headers actions proxy_fcgi alias
bash: a2enmod: command not found

 

Have you installed 6 systems with different OS each time?

I do not use the development version, the released stable version is supported and works reliably. The development versions have bad days when they just do not work. So if you want a system that works, do not use the development version. It is meant for those that do ISPConfig development or do troubleshooting to find bugs before release.
If I were you, I would install a 7th system, this time with release ISPConfig version 3.1.15.
If you really want to fix the installation you have now, I do not understand this:

What is not working? When you create a mailbox, it should have one message right away, automatically sent by ISPConfig. So if mailbox is completely empty something is wrong. Is this what you meant? Or that mailbox can not receive e-mails?
Please show complete htf_report.txt, not just short excerpt. If what you showed was all you got, remember to run the script as root user or sudo -s first.

 

Have a look at the mail log. Can be accessed via ISPC interface -> Monitor -> Mail log