How to Fix Email Attachments Not Sending in Microsoft 365
Question details
The user is unable to send email attachments through Microsoft 365 and needs troubleshooting steps to resolve the issue.
- Product
- Microsoft 365
- Device & OS
- not provided
- Scenario
- Attempting to send an email with an attached file, but the attachment is blocked or the email fails to deliver.
- Observed behavior
- The email fails to send due to attachment issues such as excessive file size, restricted file formats, or account policies.
Verify that your internet connection is stable and ensure you are not trying to send sensitive or confidential documents in an unsecured public forum.
Check Attachment Size, Format, and File Name
Ensure your file complies with Microsoft 365 email policies to prevent automatic blocking or delivery failure.
Microsoft 365 imposes specific restrictions on email attachments to ensure server stability and protect users from malicious software. Files that are too large or have restricted extensions will automatically fail to send.
Check that the total size of all your attached files is under 20 MB for desktop clients or 35 MB for webmail, which is the default limit for most Microsoft 365 accounts.
Ensure you are not attaching restricted file types such as .exe, .bat, .vbs, or .cmd. If necessary, compress these files into a .zip folder before attaching.
Right-click the file on your computer, select 'Rename', and remove any special characters or unusually long strings from the file name, then attempt to attach it again.
Try Sending via Outlook on the Web
Use the web-based version of Microsoft 365 to bypass potential glitches with your local email application.
Contact Support or Your IT Administrator
Reach out for technical assistance if your attachments are being blocked by organization-level policies or persistent account issues.
Easily Compress and Manage Documents with WPS Office
While email attachment limitations are controlled by your mail provider, managing document sizes shouldn't be difficult. WPS Office is a free, powerful productivity suite that helps you reduce file sizes, convert documents to PDF, and manage all your files seamlessly before sending them.
- 1. Download and install: Get WPS Office for free from the official website and install it on your computer.
- 2. Open your document: Launch WPS Office and open the large or restricted document you are trying to email.
- 3. Convert or compress: Use the built-in 'Export to PDF' tool or document compression features to reduce the file size, making it ready to successfully attach to your email.
Frequently Asked Questions
What is the maximum attachment size limit in Microsoft 365?
By default, the maximum message size (including all attachments) in Microsoft 365 is 35 MB for Outlook on the web and 20 MB for the Outlook desktop client, though IT administrators can adjust these limits.
Why does Microsoft 365 say my file type is blocked?
Microsoft automatically blocks specific file types, such as executable files (.exe, .cmd) and certain scripts (.vbs), because they carry a high risk of containing malware. You can bypass this by compressing the file into a .zip folder.
Can I bypass the email attachment limit by using a cloud link?
Yes. If your file exceeds the standard email attachment limits, you can upload the file to a cloud storage service like OneDrive or SharePoint, and share the generated link directly in the body of your email.
Will copying the document text into the email body help?
Yes. If you are struggling to send a small document as an attachment due to format restrictions or software glitches, opening the file, copying the text, and pasting it directly into the email body is a practical temporary workaround.
