I am also having very similar problems to this thread. My set up is running Fedora core 5 with Ispconfig v2.2.9. Installed as per howtoforge instructions.
I also can receive and send mail internally but not externally. This might be because my isp may be blocking port 25, but a few errors are showing in the mail log.
I think the problem may be because of the error.
postfix/qmgr: fatal: specify a password table via the 'smtp_sasl_password_maps'
The file 'smtp_sasl_password_maps' dosn't exist on my system or is this something that should be set up from ispconfig.
Many thanks in advance for any help you may be able to give.
PS I am new to linux and learning very quick lol