It seems that greylisting is turned on by default in Snow Leopard server which causes inbound e-mails to hang in limbo. I found a web page with the fix:
If you wish to turn it off you can disable anti-spam measures in Server Admin. To specifically only stop Greylisting do the following:
Edit /etc/postfix/main.cf and change:
smtpd_recipient_restrictions = permit_sasl_authenticated permit_mynetworks reject_unauth_destination check_policy_service unix:private/policy permit
to
smtpd_recipient_restrictions = permit_sasl_authenticated permit_mynetworks reject_unauth_destination permit
Basically delete check_policy_service unix:private/policy
When done issue:
sudo postfix reload
(Fix found on this page: http://osx.topicdesk.com/content/view/144/45/)
