Maximum receive message size

Question

Dear Everyone,

I config limit for send and receive message 15Mb, need this configure working only when employee send or received to outside organization but in inside organization working without limit.

Can do it?

Exchange 2016 CU19

Answer 1

First: Set the Max Send and Receive Size for the org to "unlimited"

https://learn.microsoft.com/en-us/exchange/mail-flow/message-size-limits?view=exchserver-2019#organizational-limits

https://learn.microsoft.com/en-us/powershell/module/exchange/set-transportconfig?view=exchange-ps
A valid value is a number up to 1.999999 gigabytes (2147482624 bytes) or the value unlimited.

Next: Create transport rules that block messages to and from your org if they are greater than 20MB. Why 20?

Base64 encoding increases the size of messages by approximately 33%, so specify a value that's 33% larger than the actual maximum message size that you want to enforce. For example, the value 64 MB results in a maximum message size of approximately 48 MB.

2 rules
One for inbound

One for outbound:

Answer 2

You can also set limit for connectors that inbound/outbound message would go through, the following example is for default settings:
Inbound:
Set limit for "Default Frontend <Mailbox server name>":

Outbound:
Set limit for the send connector that you use to send externally:

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