dpkg: error processing package sendmail-base

I upgraded to 18.10. Now I have a problem with apt. It seems to be a problem with the sendmail-base package:

sudo apt autoremove 
Reading package lists... Done
Building dependency tree       
Reading state information... Done
0 upgraded, 0 newly installed, 0 to remove and 0 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) ...
Saving current /etc/mail/sendmail.mc,cf to /var/backups
update-inetd: warning: cannot add service, /etc/inetd.conf does not exist
update-inetd: warning: cannot add service, /etc/inetd.conf does not exist
update-inetd: warning: cannot add service, /etc/inetd.conf does not exist
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)

sudo apt remove sendmail-base
Reading package lists... Done
Building dependency tree       
Reading state information... Done
The following packages will be REMOVED:
  sendmail-base
0 upgraded, 0 newly installed, 1 to remove and 0 not upgraded.
1 not fully installed or removed.
After this operation, 867 kB disk space will be freed.
Do you want to continue? [Y/n] 
(Reading database ... 650513 files and directories currently installed.)
Removing sendmail-base (8.15.2-11) ...
update-inetd: error: --group is only relevant with --add
dpkg: error processing package sendmail-base (--remove):
 installed sendmail-base package pre-removal 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)

I had similar errors: update-inetd: error: --group is only relevant with --add.

So I followed advice in the link OP gave above.

I did this:

• edited sendmail's pre-removal script /var/lib/dpkg/info/sendmail-base.prerm accordingly (depends on the error you're getting) ...I removed --group MAIL from that problem line, was almost at the top of the file
• uninstalled sendmail-base and sendmail-bin (though this may be unnecessary... I had so many errors relate to sendmail that I just nuked it... don't need it on my ubuntu desktop anyway)
• installed lsb-invalid-mta which is a fake MTA (will avoid problems later on with apps that want an MTA) - only necessary if sendmail was removed above

Now apt is upgrading properly again!