Disable AutoSSL renewal for email hosted elsewhere (Google Suite, Office365, Zoho etc.)
The AutoSSL system will automatically check every active domain name on your hosting account and it will attempt to install a new SSL certificate for any domains that do not already have one. Since October 2017, the cPanel system will notify you if an upcoming AutoSSL renewal will result in a "reduction of coverage", in other words the contact person listed in cPanel will be emailed if AutoSSL looks like it cannot be renewed on one or more of your domains / sub-domains.
If you have a cPanel hosting account for DNS and website, but the email service is pointing to a third party provider (Google Suite, Office365, Zoho) then you'll need to disable AutoSSL on the mail & autodiscover sub-domains that do not require it, or disable the notifications altogether.
To disable AutoSSL on specific domains or sub-domains, login to your cPanel control panel and navigate to the Security => SSL/TLS Status page. You'll see a list of all the domains on your account. Simply click the "Exclude from SSL" option beside each domain / sub-domain. To quickly disable AutoSSL for ALL the domains on your cPanel account, use the checkboxes on the left to select all domains and click the button "Exclude domains from AutoSSL".
To disable AutoSSL notifications only (but still have AutoSSL run in the background), login to your cPanel control panel and navigate to the Preferences => Contact Information page. Scroll down and you'll see 4 notification options beginning "AutoSSL..." - uncheck the 4 boxes and click the Save button.