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How to Fix Outlook for Mac Error 19738 for Large Attachments
Question details
The user is unable to send an email in Outlook for Mac due to error code 19738 and a Non-Delivery Report (NDR) stating the attachment is too large.
- Product
- Outlook for Mac
- Device & OS
- macOS
- Scenario
- Attempting to send an email containing large attachments through an Exchange account.
- Observed behavior
- The outgoing message fails to send, triggering error 19738 and generating an NDR because the total message size exceeds the Exchange organization or mailbox limits.
Check the total file size of your email attachments and compare it with your organization's maximum allowed message size before proceeding.
Reduce or Compress the Attachment Size
The quickest way to bypass the size limit is to reduce the file size by compressing it before attaching.
Compressing your files into a ZIP folder significantly reduces their size, which often brings the total message size below the Exchange limit.
Open Finder on your Mac and navigate to the file you want to attach.
Right-click (or Control-click) on the file and select 'Compress [File Name]' from the context menu.
Open Outlook for Mac, create a new email, and attach the newly created .zip file instead of the original.
Use a Cloud-Sharing Link
Upload your large files to a cloud service and share the link, bypassing the Exchange attachment limits entirely.
Request an Exchange Limit Increase
If organizational policy permits, your IT administrator can increase the allowed message size for your mailbox.
Try WPS Office for Seamless Document Sharing
If you frequently struggle with Outlook's attachment limits, WPS Office offers a smarter way to manage and share documents. As a free and lightweight Microsoft Office alternative, it features built-in cloud storage so you can easily send file links instead of bulky attachments.
- 1. Download WPS Office: Visit the official WPS website and download the free installer for your Mac.
- 2. Save to WPS Cloud: Open your large document in WPS Office and save it directly to your integrated WPS Cloud space.
- 3. Share via Link: Click the Share button to generate a secure link, and paste it into your email instead of attaching the file.
Frequently Asked Questions
Why am I getting error 19738 even though my file is under 20MB?
Exchange administrators can set custom organization-wide or mailbox-specific message-size limits. This means your specific organization's limit might be lower than the standard default size.
Does dragging and dropping files reduce their size in Outlook for Mac?
No, dragging and dropping a file attaches it at its original size. You must compress the file manually using your Mac's Archive Utility or a third-party compression tool to reduce its footprint.
Can I change the attachment size limit myself to fix the NDR?
No, the limit causing error 19738 is enforced at the Microsoft Exchange server level. Only your IT or Exchange administrator has the necessary permissions to increase this limit.
