I have a new server since few month ago with iRedMail, it all works well with Postfix 2.6.6 on CentOS MySQL
Linux 2.6.32-431.11.2.el6.x86_64 #1 SMP Tue Mar 25 19:59:55 UTC 2014 x86_64 x86_64 x86_64 GNU/Linux

# postconf -d | grep mail_version
mail_version = 2.6.6
milter_macro_v = $mail_name $mail_version

couple of days I noticed this on yum update[1];

I don't understand what yum is telling me:
'updated'
'an update'

is it going to update 2.6.6 to 2.6.6-2.3 ?
why is it offering 2.11 ?

apologies for asking dumb questions, thank for any pointers and suggestions

[1]# yum update
Resolving Dependencies
--> Running transaction check
---> Package postfix.x86_64 3:2.6.6-2.3.el6 will be updated
---> Package postfix.x86_64 3:2.11.0-0.el6 will be an update
--> Finished Dependency Resolution

Dependencies Resolved

======================================================
Package         Arch           Version                  Repository        Size
======================================================
Updating:
postfix         x86_64         3:2.11.0-0.el6           iRedMail          15 M

Transaction Summary
=======================================================
Upgrade       1 Package(s)