Zimbra 4.0.3 Open Source.

I need to change sender addresses for all outgoing messages. J.Doe@olddomain.com should become JDoe@newdomain.com in every outgoing message. I saw this mentioned here but it works only for web UI. The same is for setting reply-to address directly in web UI. I need to rewrite senders addresses not just in messages sent from web UI but in messages sent from offline clients (Outlooks) too. Is this possible?

I went through Postfix documentation concerning my needs and it looks like Postfix can do it, but I am quite lost in all Postfix parameters and I am not sure how much it is affected or it affects Zimbra.

Can somebody help?