[Dovecot] can't receive mail from other hosts

[carpenter at strongs.org]

i'm running RHEL v 5 and 1.0-1.2.rc15 of dovecot and 2.3.3-2 of postfix. 
users can send mail to outside hosts, but can not receive them.  i find no
errors in the maillog -- i used a page from the redhat docs to configure
postfix and dovecot so that they used the same mail directory... i
think...

any ideas on how to debug and/or fix this would be greatly appreciated.

thanks,
steve