Exchange 2016 - Application getting 4.5.2 Too Many Recipients error

Question

We have a third-party application that is sending out emails to our users via a scheduled task, and it's reporting a server response of 4.5.2: Too Many Recipients when trying to send them out.

The email was being sent to 421 recipients. Our Exchange 2016 environment was set at the default 500 recipients. I bumped that up to 700 to see if it'd make a difference, but it still reported the error the next time the task ran.

Our setup is two Exchange 2016 CU16 servers set up in a DAG. We have a load balance appliance by Kemp which hosts the virtual IP that the application is connecting to. I do not see anything on the Kemp that would report this error (and didn't expect to, as it's forwarding SMTP traffic to one of the Exchange 2016 servers).

Is there another place I should check for this recipient limit? I was verifying/changing it via the Get/Set-TransportConfig command with MaxRecipientEnvelopeLimit.

Answer 1

Ah, yes. I'd forgotten about that. Not sure why I was focusing on the Send Connector and not the Recipient Connector. ><

I'll give this a shot and report back, but I'm sure that's it.

Answer 2

Check the receive connector on all the Exchange Servers that receive these messages
The Default is 200:

-MaxRecipientsPerMessage
The MaxRecipientsPerMessage parameter specifies the maximum number of recipients per message that the Receive connector accepts before closing the connection.

A valid value is from 1 to 512000. The default value is 200.

if you want, set it higher:

https://learn.microsoft.com/en-us/powershell/module/exchange/set-receiveconnector?view=exchange-ps

Example:

Set-ReceiveConnector -Identity <'IdentityName'> -MaxRecipientsPerMessage 1000

Answer 3

Hi JoeGrover, have you tried to set a higher value for receive connector? Was the error reported after that?
According to the the official doc How recipient limits work together, the error should be resolved by modifying the value MaxRecipientsPerMessage.
If still exsits, please check the value for mailbox(by defalut it's set to unlimited):

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Get-Mailbox User1|fl name,RecipientLimits