Exchange 2016 Send & Receive Connectors & limitations

Question

Hi

We are documenting mail flow with our Exchange 2016 environment. There are a few clarifications we need with connector configurations

Receive Connectors:-

• Organization Max Receive message size is 37 MB
  a) Client Frontend MBS01 & Client Proxy MBS01 - 20 MB (IMAP & POP are not allowed)
  b) Default Frontend MBS01 Max Receive message size is 37 MB (Configured to receive mails only from SMTP gateway Ironport Appliances)
  c) Default RHOE16MBX01 Max Receive message size is 19 MB (even though this is configured as 19 MB we are receiving 37 MB mails from internet, how this works?)

Our actual requirement is to receive 37 MB mails, does the above configuration looks fine or do we have make changes with default connectors? How this affect internal users?

Send Connectors:-

• Organization Max Send message size is 28 MB
  a) Internet connector is configured with 20 MB (uses smart host)

Here our requirement is to allow 28 MB internally & externally. Do we need to change the internet connector?

Thanks in advance

Answer 1

My suggestion. Keep it simple.
Set ALL the connectors and the org Send and Receive ( both of them) to the same value. In other words set everything to 37MB.
The organization max send and receive should always be the as this applies to anonymous messages and messages to and from the internet.

Get-TransportConfig -MaxReceiveSize  37MB -MaxSendSize 37MB  

If you want to send only 20 MB to the internet then set that limitation on the send connector itself, however, it doesn't really make sense to allow 37MB from the internet but restrict sending to the internet to 20MB.

If you really want internal users to only send 28MB, use a transport rule instead ( though I would recommend not doing that since you have the org max set to 37MB)

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

Answer 2

Hello Andy

We found that to receive 37 MB mails from outside, we have to make both MaxReceiveSize & MaxSendSize as 37 MB (actually 37 MB + additional 33% ~49 MB). Why we should increase the global send size in receiving 37 MB? We are not getting the idea / config behind that

Answer 3

Thanks a lot Andy David, it's clear..