You may want your Postfix server to relay through other servers that require SMTP authentication. In addition to requiring passwords on your own server, you can configure Postfix to provide login names and passwords when relaying mail through other SMTP servers.
You have to provide Postfix with a password file that contains the
credentials it should use when authenticating to other servers. Entries
in the password file contain a domain or hostname, username, and
password in the form:
username:password. For the domain or hostname, Postfix
first checks for the destination domain from the recipient address. If
it doesn't find the domain, it then checks for the hostname it is
connecting to. This allows Postfix to work easily with sites that have
multiple MX hosts that share the same user database. Use
smtp_sasl_password_maps parameter to specify where your password file is.
smtp_sasl_security_options parameter works just like server
smtpd_sasl_security_options (discussed earlier
in the chapter) for the SMTP servers. If you don't specify any options,
the default allows all available mechanisms including plaintext but not
Use the following steps to configure Postfix to provide a login and password when relaying mail. In this example, you'll set up two different passwords for Postfix to authenticate when relaying through any server for the domain ora.com and through a host called ...