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

Maintaining user accounts in an LDAP directory is an authentication and account management strategy, but it is not a direct security hardening technique for the sendmail server's daemon or protocols against common vulnerabilities.

Enabling TLS (Transport Layer Security) encrypts mail traffic and authentication, protecting sensitive information from interception during transmission.

Disabling the VRFY (verify) command prevents attackers from querying the server to discover valid user accounts, which can be used for spamming or other targeted attacks.

Running sendmail in a chroot'd environment isolates the mail server process to a restricted portion of the filesystem, thereby limiting the scope of damage if the server is compromised.

Disabling USRLKUP is not a commonly recognized or primary security hardening technique for sendmail servers; the other options provide more direct and impactful security improvements.