mail --show-config-options
VERSION=2.2     - Version of this package
SYSCONFDIR=/etc     - System configuration directory
MAILSPOOLDIR=/var/mail/     - Default mail spool directory
SCHEME=mbox     - Default mailbox type
LOG_FACILITY=mail     - Default syslog facility
USE_LIBPAM     - PAM support
HAVE_LIBLTDL     - a portable `dlopen' wrapper library
WITH_GDBM     - GNU DBM
WITH_GNUTLS     - TLS support using GNU TLS
WITH_GSASL     - SASL support using GNU SASL
WITH_GSSAPI     - GSSAPI support
WITH_GUILE     - Support for Guile as extension language
WITH_PYTHON     - Support for Python as extension language
WITH_PTHREAD     - Support for POSIX threads
WITH_READLINE     - GNU Readline
HAVE_MYSQL     - MySQL
WITH_LDAP
WITH_LIBWRAP     - Support for TCP wrappers
ENABLE_VIRTUAL_DOMAINS     - Support for virtual mail domains
ENABLE_IMAP     - IMAP4 protocol support
ENABLE_POP     - POP3 protocol support
ENABLE_MH     - MH mail storage support
ENABLE_MAILDIR     - Maildir mail storage support
ENABLE_SMTP     - SMTP protocol support
ENABLE_SENDMAIL     - Sendmail command line interface support
ENABLE_NNTP     - NNTP protocol support