My Email Attachment Won't Send (Size Limit)

My Email Attachment Won't Send (Size Limit)

Microsoft 365 enforces a maximum email message size of 25 MB (after encoding, the effective attachment limit is approximately 20 MB). If your attachment exceeds this limit, Outlook will block the send. This is a platform-wide limit and cannot be changed per user.

How to Send Large Files Instead

  1. Use OneDrive sharing (recommended). Instead of attaching the file, upload it to OneDrive and share a link:
    • In a new email, click Attach File > Browse web locations > OneDrive.
    • Select your file and choose Share as a OneDrive link.
    • Set permissions (e.g., "Anyone with the link can view" or restrict to specific people).
  2. Use SharePoint. If the file belongs to a project or team, upload it to the appropriate SharePoint document library and share the link in your email.
  3. Compress the file. Right-click the file in File Explorer, select Send to > Compressed (zipped) folder. If the compressed version is under 20 MB, you can attach it normally.

Why OneDrive Links Are Better Than Attachments

Sharing via a link keeps the file in one place and ensures the recipient always has the latest version. It also avoids filling up the recipient's mailbox with large files and allows you to revoke access later if needed.

Need help? Submit a ticket and a CMO IT Services technician will assist you.

    • Related Articles

    • How to Create an Email Signature

      A consistent email signature presents a professional image and gives recipients your contact information at a glance. You can set up signatures in both the Outlook desktop app and Outlook on the Web. If your organization provides a standard signature ...

    • How to Report a Phishing or Suspicious Email

      Phishing emails are one of the most common attack methods used against businesses. Reporting a suspicious email does two things: it protects you by letting CMO IT Services investigate, and it helps us improve filtering so similar emails are caught ...

    • How to Set Up Your Email on a Mobile Device

      The recommended way to access your work email on a phone or tablet is through the Microsoft Outlook app. Your organization's security policies require mobile devices to be enrolled in device management before accessing work data, so you may be ...

    • Email Quarantine: How to Review Blocked Messages

      Your organization's email security filter automatically quarantines messages that appear to be spam, phishing, or contain suspicious content. Occasionally, a legitimate email may be caught by these filters. You can review your quarantined messages ...

    • Outlook Is Not Receiving or Sending Email

      When Outlook stops sending or receiving email, the issue is usually a connection problem between Outlook and Microsoft 365. Common causes include network interruptions, an expired password, a stuck Outlook profile, or a corrupt local data file. Most ...