Because I save all my mail, my mailbox is too large to leave on the server. As a result, I setup a local server on my desktop to use strictly as an archive. When I reply to messages in the archive, the default is to use the archive "email address" as the From address, which is bogus as it has to be different from my real address. As a result, in Thunderbird, I set up a bogus outgoing server so that the send would fail unless I changed the address to what it ought to be. I suppose I could create a valid alias and use that, but that could be confusing to people. Unfortunately, zimbra requires an outgoing server to be configured, and requires that it actually work as well. I think I can use "Persona" to solve my particular problem (perhaps in an even better way than my tbird hack), but I can conceive of other uses for a receive only mailbox, and think the requirement to configure an outgoing server should be removed.