This is a simple how-to to configure SMTP authenication in Sendmail.
1. install sendmail-cf rpm
#> yum install sendmail-cf
2. edit /etc/mail/sendmail.mc, verify it contains the following options
define(`SMART_HOST’, `cluster9out.us.messagelabs.com’)dnl
define(`confAUTH_OPTIONS’, `A’)dnl
TRUST_AUTH_MECH(`LOGIN PLAIN’)dnl
define(`confAUTH_MECHANISMS’, `LOGIN PLAIN’)dnl
dnl DAEMON_OPTIONS(`Port=smtp,Addr=127.0.0.1, Name=MTA’)dnl
3. execute this command
#> cd /etc/mail
#> make
#> service sendmail restart
#> /usr/sbin/saslauthd -a shadow
4. edit /etc/rc.d/rc.local, add the line below
/usr/sbin/saslauthd -a shadow