I've got some of the hints that I mentioned I've tried already from them.
# apt remove sendemail
Reading package lists... Done
Building dependency tree
Reading state information... Done
Package 'sendemail' is not installed, so not removed
0 upgraded, 0 newly installed, 0 to remove and 2 not upgraded.
1 not fully installed or removed.
After this operation, 0 B of additional disk space will be used.
Setting up sendmail-base (8.15.2-11) ...
Usage: update-inetd [<option>...] <command> <argument>
Commands:
--add <entry-line> add <entry-line>
--remove <entry-regex> remove <entry-regex>
--enable <service>[,...] enable <service> (comma-separated list)
--disable <service>[,...] disable <service> (comma-separated list)
Options:
--group <group-name> add entry to section <group-name>
--pattern <pattern> use <pattern> to select a service
--comment-chars <characters> use <characters> as comment characters
--multi allow multiple removes/disables
--file <filename> use <filename> instead of /etc/inetd.conf
--verbose explain what is being done
--debug enables debugging mode
--help display this help and exit
--version output version information and exit
In order to prevent the shell from changing your <entry-line> definition you
have to quote the <entry-line> using single or double quotes. You can use tabs
(tab character or \t) and spaces to separate the fields of the <entry-line>.
Note: users must use --comment-chars '#' to disable a service for that setting
to survive upgrades. Package maintainer scripts should use the default
--comment-chars. See update-inetd(8) for details.
Usage: update-inetd [<option>...] <command> <argument>
Commands:
--add <entry-line> add <entry-line>
--remove <entry-regex> remove <entry-regex>
--enable <service>[,...] enable <service> (comma-separated list)
--disable <service>[,...] disable <service> (comma-separated list)
Options:
--group <group-name> add entry to section <group-name>
--pattern <pattern> use <pattern> to select a service
--comment-chars <characters> use <characters> as comment characters
--multi allow multiple removes/disables
--file <filename> use <filename> instead of /etc/inetd.conf
--verbose explain what is being done
--debug enables debugging mode
--help display this help and exit
--version output version information and exit
In order to prevent the shell from changing your <entry-line> definition you
have to quote the <entry-line> using single or double quotes. You can use tabs
(tab character or \t) and spaces to separate the fields of the <entry-line>.
Note: users must use --comment-chars '#' to disable a service for that setting
to survive upgrades. Package maintainer scripts should use the default
--comment-chars. See update-inetd(8) for details.
Usage: update-inetd [<option>...] <command> <argument>
Commands:
--add <entry-line> add <entry-line>
--remove <entry-regex> remove <entry-regex>
--enable <service>[,...] enable <service> (comma-separated list)
--disable <service>[,...] disable <service> (comma-separated list)
Options:
--group <group-name> add entry to section <group-name>
--pattern <pattern> use <pattern> to select a service
--comment-chars <characters> use <characters> as comment characters
--multi allow multiple removes/disables
--file <filename> use <filename> instead of /etc/inetd.conf
--verbose explain what is being done
--debug enables debugging mode
--help display this help and exit
--version output version information and exit
In order to prevent the shell from changing your <entry-line> definition you
have to quote the <entry-line> using single or double quotes. You can use tabs
(tab character or \t) and spaces to separate the fields of the <entry-line>.
Note: users must use --comment-chars '#' to disable a service for that setting
to survive upgrades. Package maintainer scripts should use the default
--comment-chars. See update-inetd(8) for details.
update-inetd: error: --group is only relevant with --add
dpkg: error processing package sendmail-base (--configure):
installed sendmail-base package post-installation script subprocess returned error exit status 255
Errors were encountered while processing:
sendmail-base
E: Sub-process /usr/bin/dpkg returned an error code (1)