# apt install sendmail
Reading package lists... Done
Building dependency tree
Reading state information... Done
The following additional packages will be installed:
  procmail sendmail-bin sendmail-cf sensible-mda
Suggested packages:
  sendmail-doc rmail sasl2-bin
The following NEW packages will be installed:
  procmail sendmail sendmail-bin sendmail-cf sensible-mda
0 upgraded, 5 newly installed, 0 to remove and 2 not upgraded.
1 not fully installed or removed.
Need to get 0 B/1,576 kB of archives.
After this operation, 3,345 kB of additional disk space will be used.
Do you want to continue? [Y/n]
Selecting previously unselected package sendmail-cf.
(Reading database ... 1562333 files and directories currently installed.)
Preparing to unpack .../sendmail-cf_8.15.2-11_all.deb ...
Unpacking sendmail-cf (8.15.2-11) ...
Selecting previously unselected package sendmail-bin.
Preparing to unpack .../sendmail-bin_8.15.2-11_amd64.deb ...
Unpacking sendmail-bin (8.15.2-11) ...
Selecting previously unselected package procmail.
Preparing to unpack .../procmail_3.22-26_amd64.deb ...
Unpacking procmail (3.22-26) ...
Selecting previously unselected package sensible-mda.
Preparing to unpack .../sensible-mda_8.15.2-11_amd64.deb ...
Unpacking sensible-mda (8.15.2-11) ...
Selecting previously unselected package sendmail.
Preparing to unpack .../sendmail_8.15.2-11_all.deb ...
Unpacking sendmail (8.15.2-11) ...
Setting up procmail (3.22-26) ...
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
Processing triggers for systemd (239-7) ...
Setting up sendmail-cf (8.15.2-11) ...
Processing triggers for man-db (2.8.4-2) ...
dpkg: dependency problems prevent configuration of sendmail-bin:
 sendmail-bin depends on sendmail-base (= 8.15.2-11); however:
  Package sendmail-base is not configured yet.

dpkg: error processing package sendmail-bin (--configure):
 dependency problems - leaving unconfigured
dpkg: dependency problems prevent configuration of sensible-mda:
 sensible-mda depends on sendmail-bin | mail-transport-agent; however:
  Package sendmail-bin is not configured yet.
  Package mail-transport-agent is not installed.
  Package sendmail-bin which provides mail-transport-agent is not configured yet.

dpkg: error processing package sensible-mda (--configure):
 dependency problems - leaving unconfigured
dpkg: dependency problems prevent configuration of sendmail:
 sendmail depends on sendmail-base; however:
  Package sendmail-base is not configured yet.
 sendmail depends on sendmail-bin; however:
  Package sendmail-bin is not configured yet.
 sendmail depends on sensible-mda; however:
  Package sensible-mda is not configured yet.

dpkg: error processing package sendmail (--configure):
 dependency problems - leaving unconfigured
Errors were encountered while processing:
 sendmail-base
 sendmail-bin
 sensible-mda
 sendmail
E: Sub-process /usr/bin/dpkg returned an error code (1)