In the sendmail.cf file change "O PrivacyOptions=authwarnings" to this "O PrivacyOptions=authwarnings,noexpn,novrfy". What this does is prevents spammers from using the ``EXPN'' and ``VRFY'' commands in sendmail. They can be used to find and verify E-mail addresses.
In the Sendmail.cf file change "O SmtpGreetingMessage=$j Sendmail $v/$Z; $b" to this line "O SmtpGreetingMessage=$j $b". What this does is gets rid of the connection banner version number and the advert of "Sendmail".