The Outlook attachment size limit depends on your account. Free Outlook.com and Hotmail accounts allow 25 MB. Classic Outlook with Gmail, Yahoo or other IMAP/POP accounts allows 20 MB. Microsoft 365 work or school accounts allow 35 MB per sent message by default.
The limit covers all attachments in one email together. Encoding and the recipient's mail server can also make a message fail even when it is under the limit. For anything bigger, send a link instead: OneDrive handles files up to 2 GB, and a file host works without a Microsoft account.
Every figure below comes from Microsoft's own documentation, checked in November 2026.
Outlook attachment size limit: the short answer
- Outlook.com and Hotmail (free personal accounts): 25 MB.
- Classic Outlook with POP, IMAP or HTTP accounts: 20 MB, for all attachments combined.
- Microsoft 365 work or school accounts (Exchange Online): 35 MB to send and 36 MB to receive by default. An admin can raise this to as much as 150 MB.
- On-premises Exchange Server: 10 MB by default.
- OneDrive links sent from Outlook: up to 2 GB.
You may see 20, 25 or even 34 MB quoted for Outlook.com elsewhere. Microsoft's Outlook.com sending limits page (dated 04/21/2026) says 25 MB. You may also see 150 MB described as the normal Microsoft 365 allowance. It isn't. 150 MB is the highest value an admin can set, and the default is 35 MB.
Outlook attachment limits by account and app (2026 table)
| Account or app | Default limit | Can it be raised? |
|---|---|---|
| Outlook.com / Hotmail | 25 MB | No. Share from OneDrive instead (up to 2 GB) |
| Classic Outlook with POP, IMAP or HTTP accounts | 20 MB, all attachments combined | Only the Outlook-side cap, through the registry |
| Microsoft 365 work or school (Exchange Online) | 35 MB send, 36 MB receive | By an admin, from 1 MB to 150 MB |
| Outlook on the web (Microsoft 365) | 25% below the configured limit; classic attachments capped at 112 MB | Only through the admin setting |
| Outlook for iOS and Android (Microsoft 365 business and enterprise) | 33 MB | Not listed as adjustable |
| On-premises Exchange Server | 10 MB | By an admin (Maximum send size) |
| OneDrive file shared from Outlook | 2 GB | No |
Outlook.com and Hotmail (free personal accounts)
The attachment limit is 25 MB. For anything larger, Microsoft points you to OneDrive, where shared files can be up to 2 GB.
Your mailbox itself has 15 GB of email storage. That is separate from your 5 GB of Microsoft cloud storage.
Classic Outlook for Windows with Gmail, Yahoo or other IMAP/POP accounts
Outlook 2013 and later, including Outlook for Microsoft 365, sets a default limit of 20 MB (20480 KB) for internet email accounts. That covers POP3, IMAP and HTTP accounts.
This cap lives inside the Outlook program. Your email provider still enforces its own limit on top of it.
Microsoft 365 work or school accounts (Exchange Online)
Mailboxes default to 35 MB for sending and 36 MB for receiving. Admins can set a custom limit anywhere from 1 MB to 150 MB.
With an Exchange account, classic Outlook ignores its own 20 MB cap and uses the server's limit instead. The full details are on Microsoft's Exchange Online limits page, updated 2026-10-19.
Outlook on the web, Outlook for Mac, and Outlook for iOS and Android
Outlook on the web lets you send messages 25% smaller than the configured limit. Microsoft's example: if the limit is set to 100 MB, you can send messages no larger than 75 MB. Classic attachments are capped at 112 MB, while OneDrive attachments can be up to 2 GB.
Outlook for iOS and Android has a 33 MB message size limit on Microsoft 365 business and enterprise plans.
Outlook for Mac and the new Outlook for Windows: we didn't find a separate published figure from Microsoft. Go by the limit for your account type in the table above.
Why your attachment fails even when it's under the limit
Every attachment counts toward one total
The limit applies to the whole message, not to each file. Three 8 MB files add up to 24 MB. That fails in classic Outlook with a 20 MB cap, even though each file on its own is small.
Email encoding makes files about 33% bigger
Attachments are encoded when they travel as email, which makes them larger than they are on your disk. Microsoft says messages routed outside its datacenters grow by about 33%. That is why a 150 MB limit works out to a real maximum of 112 MB for mail leaving Microsoft.
A file that sits just under your limit on disk can end up over it in transit. Leave some headroom.
The recipient's mail server has its own limit
Your message has to pass every server on the way. Microsoft notes that size limits apply to inbound, outbound and internal mail. The recipient's provider has its own cap, and so does their email app.
If their limit is lower than yours, the message is rejected on their side even though Outlook sent it without complaint.
What the "bigger than the server allows" error and bounce messages mean
In classic Outlook you may see this error:
The file you're attaching is bigger than the server allows. Try putting the file in a shared location and sending a link instead.
It appears as soon as you attach something that pushes the total past your account's limit. With an on-premises Exchange mailbox, that happens by default above 10 MB, because of the server's Maximum send size setting.
A bounce, or non-delivery report (NDR), arrives after you press Send. It means a server along the way rejected the message as too large. Microsoft states that oversized messages are not delivered and the sender receives an NDR.
Can you increase the Outlook attachment size limit?
Sometimes, but only the part you control.
Classic Outlook: the MaximumAttachmentSize registry value (and what it can't fix)
For internet accounts (POP, IMAP, HTTP), you can change Outlook's own cap. Back up the registry first, because a wrong change can cause problems.
- Close Outlook.
- Open Registry Editor (
regedit). - Go to
HKEY_CURRENT_USER\Software\Microsoft\Office\16.0\Outlook\Preferences. - Create or edit a DWORD value named
MaximumAttachmentSize. - Enter the limit in KB as a decimal number. For example,
30720sets a 30 MB limit. - Restart Outlook.
This only stops Outlook from blocking the file. It does not raise your email provider's limit or the recipient's limit. If your provider rejects messages above a certain size, the email will still bounce. It also does nothing for Exchange accounts, because Outlook uses the server's limit for those.
Microsoft 365: only your admin can raise it (up to 150 MB)
On a work or school account, the limit is set on the Exchange server. Ask your IT admin, who can choose any value from 1 MB to 150 MB.
Even at 150 MB, mail leaving Microsoft is effectively capped at 112 MB because of encoding. Outlook on the web allows 25% less than the configured size. The recipient's server may refuse it anyway, so for really large files a link is the more reliable choice.
How to send a file that's too big for Outlook
Option 1: Upload to OneDrive from Outlook
In the new Outlook, Microsoft offers to upload large files to OneDrive and send a link:
- Select Attach File, then Browse This PC, and pick your file.
- Click the down arrow on the attachment.
- Choose Upload to OneDrive.
- Send the email. The recipient gets a link instead of a copy, which keeps the message small.
Files can be up to 2 GB this way. The catch: a free Microsoft account has 5 GB of cloud storage, shared between your OneDrive files and your Outlook.com attachments (per Microsoft's storage limits page, dated 09/25/2026). A few large videos can fill it, and then you'll have to delete files or pay for more.
Option 2: Compress or split the file
Zipping a folder bundles several files into one and can shrink documents. Photos and videos that are already compressed usually barely get smaller.
If the file still doesn't fit, you can split it into parts and send them in separate emails. Keep each email comfortably under the limit, remembering that the limit counts every attachment in that email. The recipient then has to download every part and reassemble them, which is clumsy for people who aren't comfortable with archives.
Option 3: Paste a download link from a file host
This works with any email account and doesn't touch your Microsoft storage. With InvisHosting, you can upload files up to 300 MB each without creating an account. You then paste the download link into your email.
You can set the upload to expire after anywhere from 1 minute to 30 days, after which it is deleted permanently. Every upload is scanned for malware with VirusTotal, and executables are blocked.
Know the limits before you rely on it:
- Anyone who has the link can download the file.
- Files are not end-to-end encrypted, so encrypt sensitive documents (for example, in a password-protected archive) before uploading. Share the password separately, not in the same email.
- Files without an expiry are kept until you delete them, unless they get no downloads for 90 days.
If the download link is long and messy in an email, run it through the link shortener. For more ways to move big files, see our guide on how to share large files for free.
Which option to choose
| Option | Max size | Account needed | Best for | Watch out for |
|---|---|---|---|---|
| OneDrive link from Outlook | 2 GB | Microsoft account | Files you already keep in OneDrive; very large files | Uses your 5 GB of free cloud storage |
| Compress or split | Your email limit per message | No | Folders of documents slightly over the limit | Media barely shrinks; split parts are awkward for recipients |
| File host link (InvisHosting) | 300 MB per file | No | Quick one-off sends, any email provider | Public to anyone with the link; encrypt sensitive files first |
| Ask your admin to raise the limit | 150 MB (112 MB outside Microsoft) | Work or school account | Regular large internal mail | Recipient servers may still reject it |
Sending large files safely
A download link is easier to forward than an attachment, so treat it with care:
- Use an expiry for anything that doesn't need to stay online. A link that dies after a week can't leak next year.
- Encrypt anything sensitive before you upload it, and send the password through a different channel.
- Tell recipients what to expect. Mention the file name and size in your email, so they can tell your link apart from a phishing message.
- Recipients should check before opening. Our guide on how to check if a file is safe walks through it.
Frequently asked questions
Is the Outlook.com attachment limit 20 MB or 25 MB?
For Outlook.com itself, it's 25 MB, according to Microsoft's support page dated 04/21/2026. The 20 MB figure is classic Outlook's default for internet accounts such as Gmail or Yahoo set up over IMAP or POP.
Does the limit apply to each file or to all attachments together?
All attachments together. Microsoft's documentation describes the error appearing for several attachments whose combined size exceeds the limit.
Can I send a 100 MB file in Outlook?
Not on a personal Outlook.com account, and not on a default Microsoft 365 account. It is possible only if your admin has raised the limit high enough. Even then, Outlook on the web allows 25% less than the setting, and the recipient's server can still reject it. A OneDrive or file host link is far more reliable.
Do OneDrive attachments use up my storage?
Yes. On a free Microsoft account, OneDrive files and Outlook.com attachments share 5 GB of cloud storage. Your 15 GB of email storage is separate.
What is the Outlook attachment limit on iPhone and Android?
On Microsoft 365 business and enterprise plans, Outlook for iOS and Android has a 33 MB message size limit.
Sources
- Sending limits in Outlook.com (Microsoft Support)
- Exchange Online limits (Microsoft Learn)
- Attachment size exceeds the allowable limit error (Microsoft Learn)
- Storage limits in Outlook.com (Microsoft Support)
- Add pictures or attach files to emails in Outlook (Microsoft Support)
This article was written with AI assistance from the sources listed above and checked automatically against them.