An administrator asked how to increase the limit on message sizes in Exchange Server.

For Exchange on-prem, the message size limit is set in the transport and on the send and receive connectors. You can also set a message size limit on specific users or groups, for example, allowing the design group to send larger messages than other employees in the organization. Note that the actual size a user can send also depends on which email client they are using. For example, Outlook 2016 for Mac is limited to 35 MB messages.

Note: Office 365 Exchange Online is configured to allow 150 MB messages, although lower limits may be set on individual mailboxes.

First, increase the size limits on the send and receive connectors and transport using the Management console or these cmdlets.

Set-ReceiveConnector "connector_name" -MaxMessageSize 30MB
Set-SendConnector "connector_name" -MaxMessageSize 30MB
Set-TransportConfig -MaxSendSize 30MB
Set-TransportConfig -MaxReceiveSize 30MB

While these examples all use the same size for all connectors, you can set different values for send and receive. The default value for the send and receive connectors and the transport is 10MB. New values can be entered as bytes or qualified with KB (kilobytes), MB (megabytes) or GB (gigabytes). Values are rounded up to the nearest KB, with a maximum value of 2147483647 (in bytes). To allow unlimited message sizes, use unlimited as the value.

Note that TransportConfig is not used on an Edge Transport server. You need to set the message size limits using the Send and Receive connectors on the Edge server.

Depending on your situation, you may also need to edit the Active Directory.

OWA 2010 Attachment Size

While we're on the subject of attachment sizes, a user had a question about OWA's file size limits. They can send 10 MB messages when they use Outlook but are limited to 5 MB when using OWA.

To change this, the admin needs to edit the web.config file on the OWA server and change the maxrequestlength value.

The web.config is at C:\Program Files\Microsoft\Exchange Server\V14\ClientAccess\Owa and can be edited using a text editor such as Notepad. Look for <httpRuntime maxRequestLength="30000" /> (it's on or about line 30) and enter a new value in KB.

After saving the file, you'll need to restart the Exchange service.