Sendmail

Some security considerations

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".

Add a smart host to relay through without running sendmail

Edit /etc/mail/submit.cf

# "Smart" relay host (may be null)

DS[192.168.1.102]

sendmail DSN: Host unknown (Name server: host not found)

This is where your relay is trying to do DNS lookups which you can disable via square brackets in sendmail.cf:

DS[164.88.15.103]