I have an process that generates over 1100 emails a day to 1100 different customers.  It generates and sends them all from one email address.
That email address has had a throttling policy applied setting every possible setting to unlimited.

I have made the following settings to the Receive connector they are coming in on.
ConnectionTimeout 00:30:00
ConnectionInactivityTimeout 00:20:00
MaxAcknowledgementDelay 00:00:00
MaxInboundConnection 10000
MaxInboundConnectionPercentagePerSource 100
MaxInboundConnectionPerSource unlimited

When we first implemented Exchange 2010, we had a similar issue, but it would fill up, and drop email.  We were able to relay through a 2003 exchange and they would not drop.

I was able to resolve that by applying a NULL throttling policy to the account and they would flow. 1100 email would be dumped from the server to exchange in 30 minutes or less.

After migrating to Exchange 2013 and removing the 2010 server, and applying the above policy changes, they emails are still only going out at 5-6 per m

Hello

tip: check smtp receive connector log for error if have..

Hi,

The MaxAcknowledgementDelay parameter should be the point. It isn't used by Microsoft Exchange Server 2013. It's only used by Microsoft Exchange 2010 servers in a coexistence environment.

Refer from:

https://technet.microsoft.com/en-us/library/bb125140(v=exchg.150).aspx

In exchange 2013, I suggest to disable the shadow redundancy to have a test. (In exchange 2010, if the MaxAcknowledgementDelay is set to 0, it disabled the shadow redundancy)

Set-TransportConfig ShadowRedundancyEnabled $false

If this change doesnt work, please change this setting back.

Best Regards.