Error code 19738 when you use Outlook for Mac to send a large email message through Exchange Server
Original KB number: 3146087
You use Microsoft Outlook 2016 for Mac or Outlook for Mac 2011 to connect to a mailbox on a Microsoft Exchange server. When you send an email message that contains a large attachment, you receive the following error messages in Outlook for Mac.
Error: Outlook cannot send the message <subject> because the message size exceeds the maximum limit set on the server. Details: The message has been moved to the Drafts folder under On My Computer. Try reducing the message size by removing or resizing any large attachments, and then resend. If the problem persists, contact your administrator. Error Code: -19738
Or, you receive a non-delivery report (NDR) in your Inbox like this one:
Subject: Undeliverable: <subject> Body: Your message wasn't delivered to anyone because it's too large. The limit is 35 MB. Your message is <size of your message>. User Name (User@domain.com) Your message couldn't be sent because it's too large.
The message contains diagnostic information for administrators, such as the following:
Remove Server returned '500 5.2.11 RESOLVER.RST.SendSizeLimit.Sender; message too large for this sender'
This issue occurs when you send an email message that's larger than the Exchange Web Services (EWS) message size limit that's configured on the Exchange server.
You can increase the message size limit on the Exchange server to allow for larger email messages to be sent from Outlook for Mac clients and other EWS clients. For more information, see the following TechNet articles as appropriate for your version of Exchange Server.
Exchange Server 2016 and 2013: Configure client-specific message size limits
Exchange Server 2010: Set message size limits for Exchange Web Services
For more information about this issue, see the following article in the Microsoft Knowledge Base:
3107326 You can't send large attachments by using the EWS client