Warning: if you can't compile Postfix because the file "db.h" isn't found, then you MUST install the Berkeley DB development package (name: db???-devel-???) that matches your system library. You can find out what is installed with the rpm command. For example:
$ rpm -qf /usr/lib/libdb.so db4-4.3.29-2
This means that you need to install db4-devel-4.3.29-2 (on some systems, specify /lib/libdb.so in the rpm query).
DO NOT download some Berkeley DB version from the network. Every Postfix program will dump core when it is built with a different Berkeley DB version than the version that is used by the system library routines. See the DB_README file for further information.
On RedHat Linux 7.1 and later procmail no longer has permission to write the mail spool directory. Workaround: chmod 1777 /var/spool/mail.
LINUX syslogd uses synchronous writes by default. Because of this, syslogd can actually use more system resources than Postfix. To avoid such badness, disable synchronous mail logfile writes by editing /etc/syslog.conf and by prepending a - to the logfile name:
/etc/syslog.conf: mail.* -/var/log/mail.log
Send a "kill -HUP" to the syslogd to make the change effective.