Changing message size limits

Problem:

You would like to change the message size limit set in Exchange Online or on your target Exchange Server. This may be helpful when uploading large items via Exchange Web Services (EWS). EWS is used by selected CodeTwo products, such as migration or backup software.

Solution:

Depending on your environment, you might need to adjust the settings of your mailboxes or edit the configuration files of Exchange Web Services (EWS) and configure the Transport Service. Click the links below to read more.

• Exchange Online (Microsoft 365)
• Exchange Server (2013 and later)

Exchange Online (Microsoft 365)

The default message size allowed in Exchange Online is up to 35 MB for sent messages and 36 MB for received messages. Both these limits can be further increased to the maximum limit of 150 MB.

Any attempt to upload items that exceed the applied size limit via EWS results in the following (or similar) errors logged to the software's mailbox log files:

Error while uploading package. System.Exception: The underlying connection was closed: An unexpected error occurred on a send. 

[ErrorMessageSizeExceeded] - The message exceeds the maximum supported size., Cannot save changes made to an item to store.

If you want to upload an item and such an error occurs, make sure this item’s size is allowed by your Exchange Online mailboxes. To do so, follow the steps below:

1. Sign in to the Exchange admin center using an account with the Organization Management or Recipient Management permissions.
2. Go to Recipients > Mailboxes and select a mailbox for which you want to manage the message size limit (Fig. 1.).

Fig. 1. Accessing mailbox settings in the Exchange admin center.

3. In the pane that opens, switch to the Mailbox tab and click Manage message size restriction (Fig. 2.).

Fig. 2. Accessing a mailbox’s message size settings.

4. In the Message size restrictions pane, set a relevant size limit for sent and received messages (Fig. 3.).

Fig. 3. Setting a message size limit for a mailbox.

5. If needed, repeat steps 2-4 for other mailboxes.

Be aware that it may take up to half an hour for the changes to take effect.

Read more about Exchange Online limits on Microsoft's website.

Exchange Server (2013 and later)

By default, the maximum size of messages received and sent in Exchange Server is 10 MB. Also, Exchange Server does not accept items larger than 64 MB to be uploaded via EWS. To change that, you need to modify the Exchange EWS web.config file(s) and configure some of the Transport Service settings via the Exchange Management Shell, as shown later in this article.

If you attempt to upload items exceeding the applied message size limit, this results in the following (or similar) errors logged to the software's log files:

• Errors caused when the maxReceivedMessageSize value is too low:

  [ErrorInvalidRequest] - The request is too large. Reduce the size of the request and try again.

• Errors caused when the requestLimits maxAllowedContentLength value is too low:

  The request failed with HTTP status 507: Insufficient Storage.

• Errors caused when the TransportConfig MaxReceiveSize value is too low or not yet set:

  [ErrorMessageSizeExceeded] - The message exceeds the maximum

Follow the solutions below to adjust the Exchange limits. We use a value of 200 MB (equal to 204800 KB or 209715200 Bytes) as an example. You can modify all values to suit your needs.

1. Log on to your target Exchange Server machine with the Client Access (CAS) role (Exchange 2013) or the Mailbox role (Exchange 2016 and later).
2. Go to your EWS settings file path:

   %ExchangeInstallPath%FrontEnd\HttpProxy\ews\web.config

3. Open the file Web.config by using any text editor.
4. Locate maxRequestLength and change its value to 204800.
5. Locate maxAllowedContentLength and change its value to 209715200.
6. Save and close the file.
7. (This step applies to Exchange 2013 only; for Exchange 2016 and later, proceed to the next step.) Restart your machine with the CAS role and log on to your machine with the Mailbox role.
8. Go to your EWS settings file path:

   %ExchangeInstallPath%ClientAccess\exchweb\ews\web.config

9. Locate maxRequestLength and change its value to 204800.
10. Locate maxAllowedContentLength and change its value to 209715200.
11. Locate all occurrences of maxReceivedMessageSize in the file and change their values, for example, to 209715200. Be aware that you don't need to change the default values of maxReceivedMessageSize for UMLegacyMessageEncoderSoap11Element bindings, as described in this Microsoft article.
12. Save and close the file.
13. Open the Exchange Management Shell (EMS).
14. To change the maximum size of received messages in the Transport Service, execute the following PowerShell cmdlet in EMS:

    Set-TransportConfig -MaxReceiveSize 200MB

15. Restart the machine, and you are good to go.

Troubleshooting

I cannot reply to or forward migrated/restored messages

There may be situations where your messages have been migrated or restored to your server, but you cannot reply to them or forward them. This behavior might be caused by the default size limits of your send/receive connectors or by the sending limits of the Transport Service. To change these settings, use the Exchange Management Shell:

1. Check your connectors' names and current settings:

   Get-SendConnector | Format-List -Property Identity, MaxMessageSize
   Get-ReceiveConnector | Format-List -Property Identity, MaxMessageSize

2. Set the limits according to your needs (e.g., to 200 MB):

   Set-TransportConfig -MaxSendSize 200MB
   Set-SendConnector -Identity "<Your Send Connector Name>" -MaxMessageSize 200MB
   Set-ReceiveConnector -Identity "<Your Receive Connector Name>" -MaxMessageSize 200MB

A message I want to migrate is too large even though the mailbox’s message size is unlimited

While you’re migrating a mailbox, some messages may be considered too large even though the mailbox’s MaxSendSize and MaxReceiveSize parameters are set to Unlimited. This may happen when the limit set for the Transport Service overrides the mailbox’s settings.

To resolve this, set a specific value for the MaxSendSize and MaxReceiveSize parameters. For instance:

Set-Mailbox -Identity "<User name>" -MaxSendSize 200MB -MaxReceiveSize 200MB

See also:

• Changing the connection speed limit
• Finding large items in Exchange mailboxes
• Troubleshooting the 'Request Entity Too Large' error

Microsoft's resources:

• Exchange Online:
  • Exchange Online limits
  • Exchange Online Protection limits
• Exchange SE/2019/2016:
  • Exchange SE/2019/2016 message size and recipient limits
  • Exchange SE/2019/2016 message rate limits and throttling  
• Exchange 2013:
  • Exchange 2013 message size limits
  • Exchange 2013 message throttling