https://migrationwiz.zendesk.com/entries/490005-how-do-i-increase-the-message-size-limits

To display current message size limits:

1. Open the Exchange Management Shell
2. Enter the following command:

Get-TransportConfig | Format-List -Property MaxReceiveSize, MaxSendSize

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

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

To increase size limits on your Exchange Server 2010 machine:

1. Open the Exchange Management Shell
2. Enter the following commands:

Set-TransportConfig -MaxReceiveSize 100MB -MaxSendSize 100MB

Get-SendConnector | Set-SendConnector -MaxMessageSize 100MB

Get-ReceiveConnector | Set-ReceiveConnector -MaxMessageSize 100MB