ETRN on secondary mx records

[mintra]

Hi

I have a number of customers with various zimbra servers in place at their premises so the primary mx points to the static ip of their adsl.

when we do maintenance or backup I want the mail to go to a secondary mx where it will be queued so that when the zimbra server goes back online it will then be forwarded to it.

The ETRN method seems to be applicable here.

How would I configure the primary mx zimbra server to request an etrn command.

Also what should I use for the secondary mx server another zimbra or something else.

Or am I just being silly and their is a better way to do this. I have done something with two zimbra servers and used fetchmail in the past. This has been useful as users can access mail in the secondary server whilst we sort out problems on the primary servers.

This however is a pain as we have to keep three sets of username password (one for each server and one for fetchmail)

Any help would be appreciated

John