There is a very good discussion about this in section 9.1.1 (The Stand Alone Config) of the Red Hat Postfix HOWTO. The key components required to setting this up are as follows:
# your ISP's SMTP server name or IP address goes here relayhost = smtprelay.someprovider.com # # this line disables spontaneous PPP connections defer_transports = smtp # # this line disables dns lookups for mail. As you are using a relay you really don't need DNS. If you use this you should use an ip address for $relayhost. disable_dns_lookups = yes |
Put the following command into your PPP or SLIP dialup scripts:
/usr/sbin/sendmail -q (whenever the Internet link is up)