MS: Exchange 2003 ports

For Exchange Communication:
Port 80 for HTTP
Port 691 for Link State Algorithm routing protocol

For Active Directory communication:
Port 389 for LDAP (TCP and UDP)
Port 3268 for Global Catalog Server LDAP (TCP)
Port 88 for Kerberos Authentication (TCP and UDP)

For DNS communication:
Port 53 for DNS (TCP and UDP)

For RPC communication:
Port 135 – RPC endpoint mapper (TCP)
Ports 1024 and higher for RPC services

If you are using IPSec between Frontend- and Backend Servers you have to open:
Port 500 for IKE (UDP)
Port 51 for Authentication Header (AH)
Port 50 for Encapsulation Protocol (ESP)

Rules for firewall

DNS
SMTP
CIFS (Both)
FE/BE Link State Routing (691)
LDAP
LDAP (GC)
LDAP (UDP)
NTP
Ping
Kerberos Sec (TCP)
Kerberos Sec (UDP)
Kerberos Adm (UDP)
RPC (All)
HTTP Exchange Link State Routing (TCP691)
RPC over HTTP Information Store (TCP6001)
RPC over HTTP DSReferral (TCP6002)
RPC over HTTP DSProxy (TCP6004)

Client Access protocols:

HTTP
HTTPS
POP3
POP3 Secure
IMAP
IMAP Secure
SMTP
SMTP Secure