go to the line (probably line# 79) where you selected
'Service = All' (you will see the following line) # You can also disable certain services (when specifying all)
now, you need to uncomment the option below
and disable the sendmail since the default MTA for cPanel is EXIM
This is not the only way to eliminate sendmail error messages in logwatch. There are other ways to eliminate the error and get the desired output in the logwatch. Let me explain if you it is worth doing. Exim and Sendmail both of them are MTAs. But for cPanel users - Exim is the default MTA that replaces Sendmail - in other words it replaces some of the options of the Sendmail. So, probably it is fair to say that Sendmail merges with Exim.
Sendmail is the original and popular MTA. It is not very user friendly or easy to configure. On the other hand, Exim is very easy to configure and also provide a better security. There is an Exim command for almost every critical Sendmail command with the same name that executes a same action. So, the scripts based on Sendmail will work perfectly with Exim and the scripts won't even know the difference. The directory structure and the files of Exim & Sendmail are same or similar or they both use the same file and directory structure. For example: /usr/lib/sendmail or /usr/sbin/sendmail or /etc/aliases.
The Exim configuration file is located in: /etc/exim/exim.conf or /etc/exim.conf - which is equivalent to sendmail.cf. The configuration file for Sendmail (sendmail.cf) is supposed to be in the directory /etc/sendmail.cf or /etc/mail/sendmail.cf. These files are not in the respective directories since Exim is the default MTA which uses Exim configuration file ('exim.conf'). The Exim users will see a file: 'submit.cf.bak' or something similar in the directory /etc/mail/ which is basically the Sendmail configuration file. This configuration file (sendmail.cf) can also be copied from the directory: /usr/share/sendmail-cf/cf/generic-linux.cf. The Sendmail package will work as a mailer by default without any configuration.
If you want to define rules with Sendmail then you need to add a list of rules - mostly under the directory /etc/mail/.
In this case, the Sendmail configuration file for logwatch is looking for your rules for relay hosts in the file /etc/mail/access. This configuration file is located in - /etc/log.d/conf/services/sendmail.conf. You can also type: 'pico -w /etc/log.d/scripts/services/sendmail' to view more details and understand how it works.
Anyway, these files (access & local-host-names) are non-existent. However, you can create the files and define the rules. For example:
'host_accept_relay' option does exactly the same thing in the case of Exim.
The other file that gives the Error message in logwatch is: 'local-host-names' - where you need to list the domains for which Sendmail is going to receive mail. This is also equivalent to the 'local_domains' option of Exim. You can create the file as follows:
pico -w /etc/mail/local-host-names
CTRL + X
You will find more details about these files in the following links:
After you configure or create any files under the directory /etc/mail/ to rebuild lookup tables for those files. You can also define different sets of rules for Sendmail under this directory (/etc/mail/). Probably, these rules are already defined in your Exim configuration file or Exim offers every option or even better choices that you can do here. In fact, the security is better with Exim.
So, my point is that it's not worth creating or configuring files for Sendmail to eliminate logwatch error messages rather it is a good idea to disable the Sendmail logging in logwatch configuration file. I hope you guys will agree with me.