I have a Windows Server 2008 R2 box hosting 3 virtual SMTP servers; vSMTP01, vSMTP02 and vSMTP03.

The first two are configured to deliver all messages to dedicated smarthosts, while the last is set to just deliver the messages on its own. All other delivery settings are as default

                                    ----(vSMTP01)-----> {SMARTHST01}
                                   /
----Inbound mail--->---SMTPSRV01---[----(vSMTP02)-----> {SMARTHST02}
                                   \
                                    ----(vSMTP03)-----> { Internet }

Now I want to take SMARTHST01 out for maintenance, but I don't want to reject submissions to vSMTP01 while doing so, so I just let it continue running.

When SMARTHST01 is no longer responding, vSMTP01 queues the messages and wait for the first retry interval to pass (15 minutes). So far so good.

Let's say SMARTHST01 gets online again after 20 minutes. The first interval has passed, and I'll have to wait another 25 minutes for the second retry interval to pass.

If I stop and start the SMTP Service (Services.msc -> Simple Mail Transfer Protocol service -> Stop), the server will retry all deliveries, but that would cause a service interruption for ALL virtual SMTP servers on the machine, which is highly undesirable.

How can I manually force vSMTP01 to retry delivery of all queued messages without interrupting the service of vSMTP02 and vSMTP03?