Installation of Courier 1.0.6-1build2 fails on Ubuntu 20.04

The installation of Courier 1.0.6-1build2 on Ubuntu 20.04 fails, although the courier-package is the one provided by the OS. The problem occurs in a post-installation script which leaves the package installed, but unconfigured and all dependent packages have issues.

The situation has been reported to Ubuntu (see https://bugs.launchpad.net/ubuntu/+source/courier/+bug/1877862), but apart from ›confirmation‹ nothing seems to happen.

Is there a workaround?

What can I provide to facilitate trouble shooting? (I'm somewhat lost.)

Add: This is the result of the installation process:

Selecting previously unselected package courier-mta.
(Reading database ... 211821 files and directories currently installed.)
Preparing to unpack .../courier-mta_1.0.6-1build2_amd64.deb ...
Adding 'diversion of /usr/bin/addcr to /usr/bin/addcr.ucspi-tcp by courier-mta'
Adding 'diversion of /usr/share/man/man1/addcr.1.gz to /usr/share/man/man1/addcr.ucspi-tcp.1.gz by courier-mta'
Unpacking courier-mta (1.0.6-1build2) ...
(Reading database ... 211980 files and directories currently installed.)
Removing libgnutls-openssl27:amd64 (3.6.13-2ubuntu1.6) ...
Setting up libnet-cidr-perl (0.20-1) ...
Setting up courier-mta (1.0.6-1build2) ...
update-alternatives: using /usr/bin/lockmail.courier to provide /usr/bin/lockmail (lockmail) in auto mode
update-alternatives: using /usr/bin/preline.courier to provide /usr/bin/preline (preline) in auto mode
'/dev/null' -> '/etc/courier/esmtpd.pem.cert'
Generating a 3072 bit RSA private key...
Generating a self signed certificate...
X.509 Certificate Information:
    Version: 3
    Serial Number (hex): 01
    Validity:
        Not Before: Mon Feb 28 07:26:38 UTC 2022
        Not After: Tue Feb 28 07:26:38 UTC 2023
    Subject: C=US,ST=NY,L=New York,O=Courier Mail Server,OU=Automatically-generated ESMTP SSL key,CN=localhost
    Subject Public Key Algorithm: RSA
    Algorithm Security Level: High (3072 bits)
        Modulus (bits 3072):
            00:cf:bb:56:4b:11:f4:74:b4:62:57:8c:9a:3b:a1:fb
            […snip…]
            9a:f7:ec:0b:53:e2:da:b6:8c:92:20:74:c7:26:8f:bd
            57
        Exponent (bits 24):
            01:00:01
    Extensions:
        Basic Constraints (critical):
            Certificate Authority (CA): FALSE
        Subject Alternative Name (not critical):
            RFC822Name: [email protected]
        Subject Key Identifier (not critical):
            c93fd83531f7869e17fc0ffd69b74e6d8679783c
Other Information:
    Public Key ID:
        sha1:c93fd83531f7869e17fc0ffd69b74e6d8679783c
        sha256:8da9285446d5dc9ccf8aa0cd4e71a620a282ae9df5920604387cba845529c87b
    Public Key PIN:
        pin-sha256:jakoVEbV3JzPiqDNTnGmIKKCrp31kgYEOHy6hFUpyHs=



Signing certificate...
Job for courier-msa.service failed because the control process exited with error code.
See "systemctl status courier-msa.service" and "journalctl -xe" for details.
invoke-rc.d: initscript courier-msa, action "start" failed.
● courier-msa.service - LSB: Courier MSA server
     Loaded: loaded (/etc/init.d/courier-msa; generated)
     Active: failed (Result: exit-code) since Mon 2022-02-28 08:26:47 CET; 16ms ago
       Docs: man:systemd-sysv-generator(8)
    Process: 2156320 ExecStart=/etc/init.d/courier-msa start (code=exited, status=2)

Feb 28 08:26:47 inet systemd[1]: Starting LSB: Courier MSA server...
Feb 28 08:26:47 inet courier-msa[2156320]:  * Starting Courier MSA server esmtpd-msa
Feb 28 08:26:47 inet systemd[1]: courier-msa.service: Control process exited, code=exited, status=2/INVALIDARGUMENT
Feb 28 08:26:47 inet systemd[1]: courier-msa.service: Failed with result 'exit-code'.
Feb 28 08:26:47 inet systemd[1]: Failed to start LSB: Courier MSA server.
dpkg: error processing package courier-mta (--configure):
 installed courier-mta package post-installation script subprocess returned error exit status 1
Processing triggers for systemd (245.4-4ubuntu3.15) ...
Processing triggers for man-db (2.9.1-1) ...
Processing triggers for libc-bin (2.31-0ubuntu9.2) ...
Errors were encountered while processing:
 courier-mta
E: Sub-process /usr/bin/dpkg returned an error code (1)
Setting up courier-mta (1.0.6-1build2) ...
Job for courier-msa.service failed because the control process exited with error code.
See "systemctl status courier-msa.service" and "journalctl -xe" for details.
invoke-rc.d: initscript courier-msa, action "start" failed.
● courier-msa.service - LSB: Courier MSA server
     Loaded: loaded (/etc/init.d/courier-msa; generated)
     Active: failed (Result: exit-code) since Mon 2022-02-28 08:27:00 CET; 17ms ago
       Docs: man:systemd-sysv-generator(8)
    Process: 2157082 ExecStart=/etc/init.d/courier-msa start (code=exited, status=2)

Feb 28 08:27:00 inet systemd[1]: Starting LSB: Courier MSA server...
Feb 28 08:27:00 inet courier-msa[2157082]:  * Starting Courier MSA server esmtpd-msa
Feb 28 08:27:00 inet systemd[1]: courier-msa.service: Control process exited, code=exited, status=2/INVALIDARGUMENT
Feb 28 08:27:00 inet systemd[1]: courier-msa.service: Failed with result 'exit-code'.
Feb 28 08:27:00 inet systemd[1]: Failed to start LSB: Courier MSA server.
dpkg: error processing package courier-mta (--configure):
 installed courier-mta package post-installation script subprocess returned error exit status 1
Errors were encountered while processing:
 courier-mta
Press Return to continue, 'q' followed by Return to quit.

So it seems, courier-msa can't be started due to an ›invalid argument‹. The syslog doesn't reveal any additional information.

Add: The courier-mta-ssl daemon seems to show a similar issue: Start fails and the syslog shows ›INVALIDARGUMENT‹.