Nothing wrecks an organized day faster than a stuck email(새 창) with an oversized attachment. When a deadline is approaching, the last thing you want is to be troubleshooting how to send an email with an attachment that exceeds the allowable size limit.

This guide covers what Outlook’s attachment limits actually are, what happens when you hit them, and how to send your large files(새 창) without the headache.

What is the Outlook attachment size limit?

Outlook’s attachment size limit depends on which version of the service you’re using. Here’s a simple breakdown:

Outlook for Microsoft 36535 MB per email
Outlook 2013-202420 MB per email
Personal Outlook accounts25 MB per email
School or work Outlook accounts25 MB per email
Exchange (on-premises)10 MB per email

This limit covers your entire email, from your attachments to your message, and any embedded images. Even if your email looks like it’s under the limit, it may still get blocked as emails sometimes increase in size as they get delivered, or if your recipient’s email server has a lower cap.

What happens when you hit the size limit? 

If you’ve attached a file that blows through the attachment size limit, Outlook will stop the message from sending and give you an error message like:

The attachment size exceeds the allowable limit.

Sometimes, Outlook doesn’t flag the problem up front. Microsoft servers sometimes reject your email and send you a bounce-back notification after you hit send. By the time the bounce-back lands in your inbox, it may already be too late. 

For businesses, that could mean a contract never gets sent and falls through instead, and on a personal level, it could mean your job application never made it to the recruiter before the deadline.

Can you increase the Outlook attachment size limit? 

Technically, yes, but you need to be comfortable with technical settings. On a Windows device, you can raise the limit of a personal Outlook account by editing the Windows Registry — but we’d recommend against this unless you really know what you’re doing, as changes can affect your computer. 

If you’re using a Microsoft 365 or Exchange account, the limit is controlled at the server level, so your IT administrator is the only one who can change it.

That said, this isn’t a reliable fix. Your recipient may not be able to receive your file if their email service doesn’t support large attachments. For most people, finding a smarter way to send large files is the more practical route; let’s explore.

How to send large files via email 

If Outlook’s file size limit is getting in the way, you still have a few good options.

Compress your files 

Compressing files into a .zip folder reduces their overall size and keeps everything tidy in one place. You can compress files right from your Windows or Mac, so there’s nothing extra to install:

  • On Windows: Right-click → Send to → Compressed (zipped) folder
  • On Mac: Control-click → Compress

This method works well for documents and folders, but it has limits. Already-compressed formats like JPEGs and MP4s won’t shrink much, and much larger files won’t compress their way under Outlook’s limit. 

For businesses, compression alone rarely cuts it, and for personal use, compressing photos and videos can lead to quality loss.

Pros:

  • Works offline and without third-party tools
  • Multiple files and folders can be packed into a single .zip file

Cons:

  • Makes little difference for large or already-compressed files
  • Compression can potentially degrade the quality of some files
  • The privacy of your .zip files is limited by the security model of your email provider

Use a file transfer service

File transfer services(새 창) let you upload a file and share a download link instead of attaching anything directly. They’re quick to use, and most don’t require an account to get started.

But their tradeoffs are worth knowing upfront. On free tiers, you have no visibility into what happens after you hit send — you can’t see who downloaded your file or revoke access if it went to the wrong person. Some services also decrypt files on their servers before re-encrypting them, meaning your data briefly exists in an unprotected state, giving the service access to it.

For businesses in regulated sectors, this can create real compliance issues with regulations like GDPR or HIPAA. For personal use, it’s worth knowing your files may pass through servers where third parties have some level of access.

Pros:

  • Quick and simple, with no account required on most services
  • Generous size limits even on free tiers

Cons:

Use cloud storage

Using cloud storage(새 창) to share files means simply uploading a file, generating a shareable link, and dropping it into your email; no attachment size limits to worry about.

For Outlook users already in the Microsoft ecosystem, OneDrive is the natural starting point. It integrates directly with Outlook and makes sharing straightforward, though its free storage is limited and shared across your Microsoft account, and you’re subjected to Microsoft’s data collection policies. This can give pause, especially when sharing personal and confidential files.

When looking for a OneDrive alternative(새 창), it’s worth thinking about how your data is handled. Some platforms, like OneDrive, can access the files you store with them, while others protect your files with end-to-end encryption(새 창) so that only you and the people you share with can see them.

For businesses, working with a non-compliant provider can expose your organization to regulatory penalties and reputational damage. For personal users, the question is simpler but still worth asking: do you want your provider to use your files for their own purposes?

Pros:

  • Bypass attachment size limits with sharing links
  • Links stay current even if you update the original file
  • Some providers offer end-to-end encryption and advanced sharing controls

Cons:

  • Privacy and security vary significantly between providers
  • Free storage tiers tend to be limited and fill up quickly
  • Misconfigured sharing permissions can expose files to unintended recipients

Securely send large files via email with Proton Drive

When Outlook blocks your attachment, Proton Drive gets your file to your recipient without compromise — no size or format restrictions, and no quality compression.

For any business that cares about privacy and access control, most sharing options come with caveats. Proton Drive is different. We protect all your files with end-to-end encryption, so only you and the people you share with can access them, not even Proton can. 

You can password-protect links(새 창), set expiry dates, track downloads, and revoke access at any time, giving you full control over who can access your files and for how long. And because Proton is based in Switzerland, your data is protected by some of the world’s strictest privacy laws.

For businesses(새 창), Proton Drive supports compliance with regulations like HIPAA(새 창) and GDPR(새 창), making it a dependable choice for regulated industries. For everyone else, it’s simply a more private and secure way to share files online.

You can get started with 5 GB of storage for free