Failed to renew Lets Encrypt certificate: One of the certificates you are going to delete is used for securing Plesk

Symptoms

• Can't renew a domain's Let's Encrypt certificate in Domains > example.com > SSL/TLS Certificates > Reissue Certificate

  Error: Let's Encrypt SSL/TLS certificate installation failed:
  Remove certificate failure: One of the certificates you are going to delete is used for securing Plesk.

• The Plesk Panel and/or mail server are secured by this domain's certificate in Tools & Settings > SSL/TLS Certificates

Cause

Plesk and/or the mail server are secured by the same certificate as the domain, so it can't be deleted.

Resolution

The recommended approach is to use different certificates for the panel/mail server and the domains.

1. Renew the panel's certificate using the server's hostname, and not any other domain name.
2. Reissue the domain's certificate normally.