Which of the following are common techniques for securing a sendmail server? (Select THREE correct answers)

Maintaining user accounts in an LDAP directory is a method for user management and authentication, but it is not primarily a direct security technique for the sendmail server's operations itself.

Enabling TLS (Transport Layer Security) encrypts communication between mail servers and clients, protecting email content and credentials from eavesdropping, which is a fundamental security practice for modern email.

Disabling the VRFY (verify) command prevents remote users from confirming the existence of user accounts on the server, thus reducing the risk of email address harvesting by spammers or attackers.

Running sendmail in a chroot'd environment isolates the mail server process and its files to a confined portion of the filesystem, significantly limiting the potential damage if the service is compromised.

Disabling USRLKUP is not a universally recognized common security technique for sendmail; the focus is generally on preventing user enumeration and enforcing secure authentication, rather than disabling a lookup feature.