Notes on sendmail smtp authentication

There are various notes around on setting up a password protected Sendmail relay box, which allows your users on one domain to send mail via sendmail in another domain, WITHOUT allowing relaying as an anti-spam measure.

Once set up, your users SMTP mail client settings require you to set a username and password.

You need to uncomment each of them, and make a few changes. Since verizon still uses plain text authentication, we need to tell Sendmail about that. After making the changes, my section in the sendmail.cf section looks like this (note the PLAIN as part of the AuthMechanism):

Once sendmail.cf is created with SMTP AUTH, you need to edit
the default-auth-info file (or create one)

Extract from sendmail.cf:
# list of authentication mechanisms
O AuthMechanisms=PLAIN GSSAPI KERBEROS_V4 DIGEST-MD5 CRAM-MD5

# default authentication information for outgoing connections
O DefaultAuthInfo=/etc/mail/default-auth-info

# SMTP AUTH flags
O AuthOptions=A


Example default-auth-info:
username
username
password
outgoing.verizon.net