452 Too many recipients from cloud email scanning vendor

We use a cloud vendor to scan all of our incoming and outgoing emails. We are starting to run in to an issue where we are sending over 100 emails in the TO, CC or BCC fields.

According to my vendor:

"By default, the  platform only accepts 100 RCPT TO entries per message body (DATA).
If the sending server issues more RCPT TO entries, then the  platform will respond with "452 Too many recipients".
This transient error code should trigger the sending mail server to provide the DATA for the first 100 recipients before it provides the next batch of RCPT TO entries."

We are using Exchange 2010 and I am not sure:
1. How to tell if my server is actually respecting the transient error and then sending them in batches.
2. If it isn't sending them in batches, how do i make it do it or does a 3rd party program exists to do this?

Has anyone come across this issue and found a solution?
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msidnamAsked:
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Adam FarageSr. Enterprise ArchitectCommented:
1. How to tell if my server is actually respecting the transient error and then sending them in batches.

As far as I know this isn't going to happen. The transport pipeline in Exchange 2010 will receive the message, and then send it out as is. This should not be done within the Exchange transport pipeline (breaking up the message) but instead within the application sending the message.

2. If it isn't sending them in batches, how do i make it do it or does a 3rd party program exists to do this?

You don't.. what is sending out these messages? You should consult the vendor of the third party application that is sending out past 100 RCPT and see if they can cut these up into smaller recipients.

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msidnamAuthor Commented:
Our developers use the Exchange API to send the emails. From my understanding they mimic what a regular use would be doing in outlook.

We use our vendor as a smarthost, so I imagine what is happening is our devs have a script or program that connects to the Exchange API, creates the message, adds the recipients and then sends the email. Exchange in turn takes that email and then sends it out through the smarthost connector.

If it's over 100 email addresses in any of the fields the vendor then sends the transient error telling exchange to "hold on?"

I got this from my vendor as well: "We just do a deferral when we get to 100 recipients, and we go ahead and deliver that. Then Exchange will reconnect and give us more recipients. It works that way by default, so they shouldn't have to do anything.
It's just 100 recpients per SMTP thread
"
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