Thanks for the great guide! After installing postfix I couldn't telnet to localhost port 25 - it connected, but no 220 or ehlo response. /var/log/syslog showed "Dec  2 20:11:40 myserver postfix/tlsmgr[5678]: fatal: open database /var/lib/postfix/smtpd_scache.db: Permission denied"

To fix it, I ran, as root,

chown postfix:postfix /var/lib/postfix/smtpd_scache.db; chown postfix:postfix /var/lib/postfix/smtpd_scache.db

I have Ubuntu 8.10 dist-upgraded from 8.04, fully patched as of Dec 2.