How can I configure Sendmail to use SMTP auth

Issue:
How can I configure Sendmail to use SMTP authentication when sending email? Resolution:To enable SMTP authentication, uncomment the following in /etc/mail/sendmail.mc by removing the dnl at the beginning of the line:

define(`confAUTH_OPTIONS‘, `A p‘)dnl
…
TRUST_AUTH_MECH(`EXTERNAL DIGEST-MD5 CRAM-MD5 LOGIN PLAIN‘)dnl
define(`confAUTH_MECHANISMS‘, `EXTERNAL GSSAPI DIGEST-MD5 CRAM-MD5 LOGIN PLAIN‘)dnl
…
DAEMON_OPTIONS(`Port=submission, Name=MSA, M=Ea‘)dnl

Restart Sendmail with the command:

# service sendmail restart

When setting up the email client, make sure the option "SMTP server requires authentication" is enabled in the Send section of the mail server configuration.

Note: SMTP authentication requires that SSL encryption is already configured. When Sendmail is restarted with these options uncommented, it assumes that secure SMTP (smtps) is running on port 465 instead of the insecure SMTP on port 25. All SMTP authentication is done over port 587.

refer: www.redhat.com