accept_unresolvable_domains
If you comment this FEATURE out, sendmail will reject mail from any source that cannot be verified via a DNS lookup. Normally, if a mail source doesn't have a DNS record, it means someone is up to no good.

redirect
allows mail to be redirected to another site. For example, if a user has moved.

always_add_domain
even on locally delivered mail, add the full domain name.

mailertable
Allow mailertable to be used to override routing decisions for particular domains (discussed below).

domaintable
Allow a domaintable to provide domain name mapping.

genericstable
Allow local address mapping to virtual domains (discussed below).

virtusertable
Allow virtual domain mapping on this host (discussed below).

nullclient
This is a host that does nothing but forward all of its mail to another host.

smrsh
Use Sendmail Restricted Shell for mailing programs.

promiscuous relay
Relay everything. The default is relay nothing.

accept_unqualified_senders
Allow local users to send mail without a supplied domain name (not a good idea).

access_db
Turn on access database to allow refusal of mail from particular hosts or domains (discussed below).

blacklist_recipients
Allows mail delivery to be disabled for certain local users, such as nobody, ftp, etc.