Question problems with mailserver under plesk

[Doro_Co]

Hello
I did try to change the mailserver, but did get errors.
after #apt upgrade i got this:

sudo apt-get upgrade
Reading package lists... Done
Building dependency tree
Reading state information... Done
You might want to run 'apt --fix-broken install' to correct these.
The following packages have unmet dependencies:
 plesk-mail-qc-driver : Depends: psa-qmail-rblsmtpd but it is not installed
 postfix-pcre : Depends: postfix (= 3.3.0-1ubuntu0.2) but it is not installed
E: Unmet dependencies. Try 'apt --fix-broken install' with no packages (or specify a solution).
doro@vmdxxxxx:/etc/apt/sources.list.d$ ^C
doro@vmdxxxxx:/etc/apt/sources.list.d$ apt --fix-broken install
E: Could not open lock file /var/lib/dpkg/lock-frontend - open (13: Permission denied)
E: Unable to acquire the dpkg frontend lock (/var/lib/dpkg/lock-frontend), are you root?
doro@vmdxxxxx:/etc/apt/sources.list.d$ sudo apt --fix-broken install
Reading package lists... Done
Building dependency tree
Reading state information... Done
Correcting dependencies... Done
The following additional packages will be installed:
  psa-qmail-rblsmtpd
The following packages will be REMOVED:
  postfix-pcre
The following NEW packages will be installed:
  psa-qmail-rblsmtpd
0 upgraded, 1 newly installed, 1 to remove and 3 not upgraded.
3 not fully installed or removed.
Need to get 0 B/21.3 kB of archives.
After this operation, 59.4 kB disk space will be freed.
Do you want to continue? [Y/n] y
(Reading database ... 263931 files and directories currently installed.)
Removing postfix-pcre (3.3.0-1ubuntu0.2) ...
/var/lib/dpkg/info/postfix-pcre.prerm: 18: .: Can't open /usr/share/postfix/postinst.functions
dpkg: error processing package postfix-pcre (--remove):
 installed postfix-pcre package pre-removal script subprocess returned error exit status 2
/var/lib/dpkg/info/postfix-pcre.postinst: 28: .: Can't open /usr/share/postfix/postinst.functions
dpkg: error while cleaning up:
 installed postfix-pcre package post-installation script subprocess returned error exit status 2
Errors were encountered while processing:
 postfix-pcre
E: Sub-process /usr/bin/dpkg returned an error code (1)

what to do?