Checking this test: http://checktls.com/perl/TestSender.pl
I think below transcript shows that although the recipient server offered TLS it was not initiated
___TRANSCRIPT BEGINS ON THE NEXT LINE___
<-- 220 ts3.checktls.com CheckTLS TestSender Sat, 23 Nov 2013 10:22:39 -0500
--> EHLO mail.domain.com
<-- 250-ts3.checktls.com Hello [xx.xxx.xxx.xx], pleased to meet you
<-- 250-ENHANCEDSTATUSCODES
<-- 250-8BITMIME
<-- 250-STARTTLS
<-- 250 HELP
--> MAIL FROM:<user@domain.com> BODY=7BIT
<-- 250 Ok - mail from user@domain.com
--> RCPT TO:<test@TestSender.CheckTLS.com>
<-- 250 Ok - recipient test@TestSender.CheckTLS.com
--> DATA
<-- 354 Send data. End with CRLF.CRLF
==== Required information ====
- iRedMail version: iRedMail-0.8.5
- Store mail accounts in which backend (LDAP/MySQL/PGSQL): MySQL
- Linux/BSD distribution name and version: CentOS 6.3
- Related log if you're reporting an issue:
====