Outlook’s default attachment size limit is 25 megabytes per email message sent through the service. If you have ever wondered what is the size limit for outlook attachments, this article gives you the full answer. You will learn the exact limits for different Outlook versions, how to send larger files, and what happens when you exceed the cap.
Most people hit this wall when trying to share a video, a high-resolution photo set, or a large PDF. The 25 MB limit applies to the total message size, including the body text and any inline images. So your actual file allowance is often less than 25 MB.
What Is The Size Limit For Outlook Attachments
Microsoft sets the default attachment size limit at 25 MB for Outlook.com, Microsoft 365, and Outlook desktop apps. This limit is not arbitrary. It balances email deliverability with server storage costs. Larger emails can bounce or get rejected by recipient servers.
Here is a quick breakdown of the limits by Outlook version:
- Outlook.com (free): 25 MB per message
- Microsoft 365 (business): 25 MB per message, but admins can increase it to 150 MB
- Outlook 2016, 2019, 2021: 25 MB per message (default)
- Outlook for Mac: 25 MB per message
- Outlook on the web (OWA): 25 MB per message
- Exchange Server (on-premises): 10 MB to 25 MB, depending on admin settings
If you use a corporate or school account, your IT administrator may have changed these limits. Always check with your IT team if you are unsure.
What Counts Toward The 25 MB Limit
The 25 MB limit includes everything in the email. That means:
- The attachment file sizes
- The email body text
- Inline images (like signatures or embedded pictures)
- Any formatting or HTML code
For example, if you attach a 24 MB file and have a 1 MB signature image, you are already over the limit. The message will not send until you reduce the total size.
What Happens When You Exceed The Limit
When you try to send an attachment larger than the limit, Outlook shows an error message. The exact wording varies by version, but it usually says something like “The file you are trying to attach is larger than the server allows.” The email will not be sent until you remove or compress the file.
If you are using Outlook.com, the system may automatically offer to upload the file to OneDrive and share a link instead. This is a built-in workaround.
How To Send Files Larger Than 25 MB In Outlook
You have several options to bypass the attachment size limit. Each method has pros and cons.
Option 1: Use OneDrive Or SharePoint
Microsoft’s cloud storage services integrate directly with Outlook. Instead of attaching a file, you upload it to OneDrive or SharePoint and insert a shareable link.
- Open a new email in Outlook.
- Click the “Attach File” icon (paperclip).
- Select “Browse this computer” or “Browse cloud locations.”
- If the file is already in OneDrive, choose it from the list.
- If not, upload it first, then select it.
- Outlook will ask: “Share as a OneDrive link” or “Attach as a copy.” Choose the link option.
- Send the email.
The recipient clicks the link to download the file. There is no size limit for OneDrive files (up to your storage quota). This method works for files up to 250 GB if you have enough space.
Option 2: Compress The File
Compressing a file reduces its size. Use built-in tools like WinRAR, 7-Zip, or Windows File Explorer’s “Send to compressed folder” feature.
- Right-click the file and select “Send to” > “Compressed (zipped) folder.”
- Check the new size. If it is under 25 MB, attach the zip file.
- If not, try a different compression method or split the file.
Compression works best for text files, spreadsheets, and PDFs. Images and videos compress less effectively.
Option 3: Split The File Into Smaller Parts
For very large files, split them into multiple smaller archives. Use tools like 7-Zip or WinRAR to create a multi-volume archive. Each part should be under 25 MB. Send each part in a separate email.
Recipients will need to download all parts and use the same tool to extract the original file. This method is clunky but works when other options are not available.
Option 4: Use A Third-Party File Transfer Service
Services like WeTransfer, Dropbox, or Google Drive let you share large files. Upload the file, get a shareable link, and paste it into the email body. Most free tiers allow files up to 2 GB.
Be aware of privacy and security risks. Do not share sensitive or confidential files this way unless the service offers encryption.
Option 5: Ask Your IT Admin To Increase The Limit
If you use a business or school account, your IT admin can raise the attachment size limit. In Microsoft 365, the maximum is 150 MB. In Exchange Server, it can be set to 25 MB or higher. This change affects all users in the organization.
Contact your IT department and explain why you need a larger limit. They may approve it for specific users or departments.
Outlook Attachment Size Limits For Different Versions
Not all Outlook versions are the same. Here is a detailed look at the limits for each major version.
Outlook.com (Free)
The free web version of Outlook has a strict 25 MB limit. You cannot change it. If you exceed the limit, Outlook automatically offers to upload the file to OneDrive. You get 5 GB of free OneDrive storage.
Microsoft 365 (Business And Personal)
Microsoft 365 subscribers have a 25 MB default limit. Admins can increase it to 150 MB via the Exchange admin center. Personal subscribers cannot change the limit themselves. Business users should ask their IT admin.
Outlook Desktop (2016, 2019, 2021)
These standalone versions also default to 25 MB. You can change the limit by editing the Windows Registry or Group Policy. This is not recommended for casual users because mistakes can break Outlook.
Outlook For Mac
The Mac version has the same 25 MB limit. There is no built-in way to increase it. Use OneDrive or a third-party service for larger files.
Outlook On The Web (OWA)
OWA uses the same limits as your Exchange or Microsoft 365 account. Typically 25 MB, but admins can adjust it.
Exchange Server (On-Premises)
If your organization runs its own Exchange server, the limit is set by the admin. Common values are 10 MB, 15 MB, or 25 MB. Some organizations set it lower to save bandwidth.
How To Check Your Current Attachment Size Limit
You can test your limit without sending a real email. Here is how:
- Create a new email in Outlook.
- Attach a file that is exactly 25 MB (or a little larger).
- Try to send it to yourself.
- If it sends, your limit is at least 25 MB. If it fails, your limit is lower.
For business accounts, check with your IT admin. They can tell you the exact limit and whether it can be changed.
Common Problems With Large Attachments
Even if you stay under the limit, large attachments can cause issues. Here are some common problems and solutions.
Email Bounces Back
If the recipient’s server has a lower limit than yours, the email bounces. Many email providers limit incoming attachments to 10 MB or 20 MB. Use a link instead of a direct attachment.
Slow Upload Or Download
Large files take time to upload and download. If you have a slow internet connection, consider compressing the file or using a cloud service.
Attachment Blocked By Security Filters
Some file types are blocked by Outlook or recipient servers. Common blocked types include .exe, .bat, .js, and .vbs. Renaming the file does not help. Use a zip archive or cloud link.
Storage Quota Exceeded
Outlook.com and Microsoft 365 have storage limits. If your mailbox is full, you cannot send or receive emails with attachments. Free up space by deleting old messages or moving files to OneDrive.
Best Practices For Sending Attachments In Outlook
Follow these tips to avoid attachment-related problems.
- Always compress files before attaching them.
- Use cloud links for files over 10 MB.
- Check the total message size before sending.
- Avoid sending executable files or scripts.
- Use descriptive file names (no special characters).
- Test large attachments with a colleague first.
Frequently Asked Questions
What Is The Maximum Attachment Size For Outlook 365?
The default is 25 MB, but administrators can increase it to 150 MB. Personal subscribers cannot change it.
Can I Send A 50 MB File In Outlook?
Not as a direct attachment. You must use OneDrive, compress the file, or split it into smaller parts.
Why Does Outlook Say My Attachment Is Too Large?
Your file exceeds the 25 MB limit (or your organization’s lower limit). Reduce the file size or use a cloud link.
How Do I Increase The Attachment Size Limit In Outlook?
For business accounts, ask your IT admin. For personal accounts, you cannot increase it. Use workarounds like OneDrive.
Does Outlook Block Certain File Types?
Yes. Outlook blocks potentially dangerous file types like .exe, .bat, and .js. Use a zip archive to send these files.
Final Thoughts On Outlook Attachment Limits
Knowing what is the size limit for outlook attachments helps you avoid frustrating errors. The 25 MB default is generous for most everyday use. When you need to send larger files, OneDrive integration is the easiest solution. Compress, split, or use third-party services as backups.
Always check the total message size before hitting send. A few extra seconds can save you from a bounced email. If you work in a corporate environment, talk to your IT admin about raising the limit if needed.
Remember that attachment limits exist for good reasons. They protect email servers from overload and reduce spam. By using cloud links for large files, you keep your email fast and reliable for everyone.
Now you have all the information you need to send attachments in Outlook without hitting the size wall. Try the methods above and see which one works best for your situation.