What should be listening on tcp port 12345?

[Robert Spellman]

I'm in the process of adding another front end server to our cyrus email 
cluster.  The new server is running RedHat ES5, and rpm shows the 
version of cyrus is cyrus-imapd-2.3.7.  Our front ends provide imaps, 
smtp (via sendmail) and lmtp.  Sendmail uses smmap to verify the 
recipients addrsess, using the process outlined within the RTCyrus3 
project.  lmtp then handles the delivery of the email to our backend 
servers.  The backend servers are running cyrus-imapd-2.2.12.

During testing of the new server, I noticed a significant delay during 
the delivery of email of up to 10 minutes.  The delay seems to be caused 
by the smmap process while it attempts to connect to tcp port 12345 on 
the backend server.  iptables on the backend server was configured to 
ignore attempts to connect on tcp port 12345.  Changing iptables to 
reject  connections to tcp port 12345 sped up the process considerably.

What process is supposed to be listening on that port? 

Here's output from /var/log/maillog.  mailstore03 is the correct backend 
server for my mailbox.

Mar 24 14:41:25 postoffice04 smmapd[31605]: executed
Mar 24 14:42:41 postoffice04 smmapd[31605]: accepted connection
Mar 24 14:42:41 postoffice04 smmapd[31605]: verify_user(user.rspell) 
proxying to host mailstore03.bates.edu
Mar 24 14:42:41 postoffice04 smmapd[31605]: verify_user(user.rspell) 
failed: can't connect to mailstore03.bates.edu


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