[CentOS] Why is iptables configured to accept packets on ports 50 and 51?

Tue May 17 18:13:16 UTC 2011
Aleksey Tsalolikhin <atsaloli.tech at gmail.com>

[root at hwdltsaloli ~]# cat /etc/sysconfig/iptables
# Firewall configuration written by system-config-securitylevel
# Manual customization of this file is not recommended.
*filter
:INPUT ACCEPT [0:0]
:FORWARD ACCEPT [0:0]
:OUTPUT ACCEPT [0:0]
:RH-Firewall-1-INPUT - [0:0]
-A INPUT -j RH-Firewall-1-INPUT
-A FORWARD -j RH-Firewall-1-INPUT
-A RH-Firewall-1-INPUT -i lo -j ACCEPT
-A RH-Firewall-1-INPUT -p icmp --icmp-type any -j ACCEPT
-A RH-Firewall-1-INPUT -p 50 -j ACCEPT
-A RH-Firewall-1-INPUT -p 51 -j ACCEPT
-A RH-Firewall-1-INPUT -m state --state ESTABLISHED,RELATED -j ACCEPT
-A RH-Firewall-1-INPUT -j REJECT --reject-with icmp-host-prohibited
COMMIT
[root at hwdltsaloli ~]# lsof -i:50
[root at hwdltsaloli ~]# lsof -i:51
[root at hwdltsaloli ~]#


/etc/services says:

re-mail-ck      50/tcp                          # Remote Mail Checking Protocol
re-mail-ck      50/udp                          # Remote Mail Checking Protocol

la-maint        51/tcp                          #
la-maint        51/udp                          # IMP Logical Address
Maintenance

Google turns up RMCP is a simple lightweight DP protocol for checking
if you have mail on a server

A quick Google search failed to turn up what is "IMP Logical Address
Maintenance"

Why is this in the default iptables configuration?

Thanks,
Aleksey