In MS Outlook, email messages often come with attachments, and the size of these attachments can vary significantly. You might be wondering: what's the default file size limit for attachments in Outlook? By default, Outlook sets a limit of 20 MB for attachments, but you can adjust this limit by making changes to the system registry settings. There are also alternative methods like file size compression, utilizing OneDrive, and splitting files. In this post, we will explore various aspects of Outlook attachments, including limitations on file sizes, restricted file extensions, and, last but not least, solutions for sending large files as attachments in MS Outlook.

Ways to Email Large Files as Attachments in Outlook

In this section, we'll delve into methods for sending large files as email attachments in Outlook. You might be wondering why many email service providers impose such strict limits on attachments. The concise answer to this is "security reasons." Without file size limits, email servers could be overwhelmed by numerous large emails, potentially causing slowdowns and disruptions to their normal operations. Now, let's explore ways to send large files as attachments in Outlook. Below is the error message you might encounter if you attempt to attach files that exceed the limitation.

error message
Method #1 Compress Attachments

The easiest way that comes to anyone’s mind is compressing attachments before sending them. Compressions can help bring down the file-size, within the predefined limitation that is 20 MB by default. The algorithms employed in compression tasks works so well that you won’t even notice any considerable difference between the original and compressed files. The tools that you need in performing compression are WinZip, WinRAR, etc. Assuming you have already installed one of these file compression tools, right-click on the file that you would like to compress and select Send to > Compressed (zipped) folder. If you now check the properties of the compressed file, then you will see a considerable difference.

Compress Attachments
Method #2 Resize Image Attachments

If your attachments are image files, then you can easily resize them in Outlook using the Resize Image feature. To do so, in your message window, select the File tab from the Outlook ribbon and select Resize large images when I send this message.

Resize Image Attachments

Note: Embedding images in the message body, you won’t be able to use the resize feature.

Method #3 Send Files Through Cloud Storage Services

If you're dealing with oversized files, there are several options to explore, such as utilizing cloud services, file-sharing platforms, or FTP websites. In this discussion, we'll focus on OneDrive, a cloud storage solution created by Microsoft. It's worth noting that with a free Outlook account, you automatically receive 15 GB of storage on your OneDrive. Should you require additional space, you can opt for a subscription plan, which provides an impressive 1 TB of storage. Below, you'll find a step-by-step guide on how to send large attachments using OneDrive:

  1. Log in to your OneDrive account using your Outlook credentials.
  2. Right-click on the file that you would like to share and click Share. click Share
  3. At this juncture, you have two choices: you can either input the email addresses of all the individuals you wish to share the file with, or you can generate a link that can be included in the email message body. you can generate a link that you can embed in the email message body If you have decided to embed the link in the email message, then you should click on the Copy Link icon.
  4. Click on the copy button. Click on the copy button
  5. Now, go to the email message > Insert tab > Links > Link. Go to the email message
  6. In the Address box, paste the earlier copied link. Paste the earlier copied link
  7. You will see that the link gets embedded in the message body, as shown below. Link gets embedded in the message body
Method #4 Using Freeware Tools Such as “Handbrake”

If you have large-sized videos to attach, consider using Handbrake, a freeware utility designed for effortless compression of your bulky video files. One can download the tool here.

The detailed Steps are outlined below:

  1. Launch the tool, and don’t get panicked by the buttons and available options.
  2. Next, click on the Open Source button to add file(s) for compression. Click on the Open Source button to add file(s) for compression
  3. Now, click on the Video tab and adjust the output video quality using the variable slider. Lower Constant Quality value signifies the lower output quality. Click on the Video tab and adjust the output video quality
  4. Now, click on the Start Encode button to initiate compression. Click on the Start Encode button to initiate compression Check the output file size. Now you can attach this compressed video file along with the mail.
Kernel for Attachment Management

Often, when recipients receive an email with attachments, they may encounter difficulties opening these attachments. This issue can stem from either file corruption or Outlook's security measures blocking certain file extensions deemed potentially risky. In such scenarios, a dependable solution like Kernel for Attachment Management proves invaluable. This tool is specifically crafted to recover lost, damaged, or blocked attachments. Additionally, users can establish multiple customization rules for extracting email attachments. We recommend trying out the trial version to become familiar with the tool's capabilities.

Kernel for Attachment Management home screen


In this post, we've explored various methods for sending large files as Outlook attachments. However, it's not uncommon for these attachments to become damaged, corrupted, or blocked by Outlook on the recipient's end. In such challenging situations, the Kernel for Attachment Management tool can prove to be immensely valuable. This tool not only facilitates the repair of damaged attachments but also enables the opening of blocked attachments in Outlook.