Exchange 2010 How To...

How to increase the maximum message size for incoming emails

To increase the maximum message size for incoming emails:

  1. Start Exchange Management Console
  2. Navigate to:
    Microsoft Exchange > Microsoft Exchange On-Premises (server) > Server Configuration > Hub Transport
  3. In the bottom pane there are two tabs, on the "Receive Connectors" tab will be listed all of the receive connectors for the server. You might have two receive connectors listed (I do), in which case one will most likely be for SMTP (TCP/IP port 25) and one for MSA (TCP/IP port 587). You may need to do the following for all the receive connectors you have, or make a judgment call as to which require it.
  4. Open the properties of the receive connector.
  5. On the "General" tab there is a box with the caption "Maximum message size (KB):", in the text box next to this is the current maximum message size for this connector.
  6. Increase this value. The number is the number of KB. The default is 10240KB (i.e. 10MB). To set this to 20MB specify 20480.
  7. Click [OK]

Gotcha: You must also do the following. Exchange considers message submission to the store drive (i.e. once it has received an email and is putting it in the appropriate inbox) as a "send" operation. So you need to check that the organisation maximum send size is at least as large. So:

  1. Still using Exchange Management Console
  2. Navigate to:
    Microsoft Exchange > Microsoft Exchange On-Premises (server) > Organization Configuration > Hub Transport
  3. Select the "Global Settings" tab.
  4. Open the properties for "Transport Settings".
  5. Ensure that the "Maximum send size (KB)" is at least equal to your new connector receive size. The default is 12000KB (i.e. a little less than 12MB).
  6. Whilst the "Maximum receive size (KB)" defaults to 40960KB (i.e. 40MB), it is worth checking that this is greater than the current connector receive size.

If you prefer to use the Exchange Management Shell, you can do all the above using the EMS. The relevant commands are:

Get-ReceiveConnector | fl name,MaxMessageSize
Will show the current "MaxMessageSize" for all of your connectors.
Get-TransportConfig | fl MaxSendSize, MaxReceiveSize
Will show the current MaxSendSize and MaxReceiveSize for the organisation.
Set-ReceiveConnector "connector-name" -MaxMessageSize 20MB
Will set the MaxMessageSize for the named connector to 20MB.
Set-TransportConfig -MaxReceiveSize 40MB -MaxSendSize 20MB
Will set the organisation transport MaxSendSize (to 20MB) and MaxReceiveSize (to 40MB).

The default out of the box settings for are 40MB for the MaxReceiveSize, and 12000KB for the MaxSendSize.

These notes have been tested with Exchange Server 2010.

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