Hanno Hecker wrote:
There's no real queueing mechanism with the smtp-forward plugin, the mail will be rejected with a temporary error, which means the mail will stay in the client's queue and sent later again... well at least for most MTAs.
If you don't have any other queue plugin loaded, you are correct. However, there is nothing to stop you from adding a second queue method (say qmail-queue) after smtp-forward. Indeed, this is how I have my inbound MX boxes configured. If the primary e-mail server is unable to receive mail, it queues up on the secondary box[es] and then gets delivered later.
The important thing to do is to make sure that the secondary queue will only accept mail that the primary queue would have normally accepted. The reason for this is otherwise you will wind up sending bounce messages when you should have refused the message during the initial conversation. This last step can be somewhat tricky to implement if your user database is on the primary mail server (which means you can't check it when that box is down). Having a distributed database is pretty much required to make this work properly...
John
