TLS failure

[FergIxico]

Hello all

I am having a problem as follows:
TLS is enabled on the Zimbra admin console however mail to domains that require it are not being delivered. I tested the connection using
CheckTLS.com: Secure eMail (TLS SMTP) OnLine Tools and Tests
and get the following included in their reply to me:

___TRANSCRIPT BEGINS ON THE NEXT LINE___
<-- 220 ts2.checktls.com CheckTLS TestSender Thu, 19 May 2011 09:07:27 -0400
--> HELO mail.ourdomain.net
****************************************
*** ********** Error Note ********** ***
*** ***
*** Sender used HELO instead of EHLO ***
****************************************

Can you please advise me as to how I can get TLS working?

Many thanks

Fergus