Exchange 2013 OWA “The following files couldn’t be attached” error

If are trying to add a large attachment to an email in Outlook Web App (OWA) you might get one of the following errors:

  • The following files couldn't be attached: Filename. Please try again later.
  • The following files weren't attached because adding them would cause the message to exceed the maximum size limit of 10 MB: filename.

As you can see from the second error, the problem is self-explanatory: the attachment is just too big. In Exchange 2013 the default maximum message size for an attachment is 10MB.

To Increase this limit you need to follow these steps:

  • Increase the maximum message size for the organization by using the Set-TransportConfig cmdlet;
  • Increase the maximum message size for the Send connectors by using the Set-SendConnector cmdlet;
  • Increase the maximum message size for the Receive connectors using the Set-ReceiveConnector cmdlet;
  • Increase the following settings in the OWA Web.config file:
      • maxAllowedContentLength (value in bytes);
      • maxReceivedMessageSize (value in bytes);
      • maxStringContentLength (value in bytes);
      • maxRequestLength (value in kilobytes).
  • Increase the following settings in the EWS web.config file:
      • maxAllowedContentLength (value in bytes);
      • maxReceivedMessageSize (value in bytes).
  • Stop and then restart the MSExchangeOWAAppPool application pool;
  • Stop and then restart the MSExchangeServicesAppPool application pool.

IMPORTANT: due to the new architecture of Exchange 2013, steps 4 and 5 must be performed in both of the following locations:

    • The Client Access server on which the Web.config files are located in the following path: %ExchangeInstallPath%\FrontEnd\HttpProxy
    • The Mailbox server on which the Web.config files are located in the following path: %ExchangeInstallPath%\ClientAccess

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