November 2026 · Folder Suggest

Outlook Attachment Size Limit: What Each Account Allows and How to Send a Larger File

Your file won’t attach, or your email came back undelivered. The limit depends mostly on your account and on the server at the other end, so the number you found online may not be yours. A link usually gets the file there, as long as the recipient has permission to open it.

In short: as of November 2026, a personal Outlook.com email can be 25 MB, though one Microsoft page says 20 MB, so stay under 20 MB to be safe. A Microsoft 365 work or school mailbox defaults to 35 MB to send and 36 MB to receive, and an admin can set it from 1 MB to 150 MB. These limits cover the whole message, and encoding can add about 33% to mail leaving Microsoft’s datacenters, so the file you can send may be smaller than the number suggests. The recipient’s server has its own limit too. For anything larger, upload the file to OneDrive or SharePoint and send a link. On Outlook.com and Outlook on the web, Microsoft lists linked files up to 2 GB, and on Outlook.com the link doesn’t count toward the email size.

Outlook Attachment Size Limit by Account and Client

From Microsoft’s Exchange Online limits, Outlook.com sending limits and classic Outlook troubleshooting article. Microsoft gives no separate figure for a personal account in Outlook for Mac. For the phone apps, its mobile page lists 33 MB for most accounts and 20 MB for iCloud.

Account and Outlook	Limit	What to know
Outlook.com (personal)	25 MB	Includes text and attachments. One Microsoft page says 20 MB
Classic Outlook, POP3, IMAP or HTTP account	20 MB in total	Set by Outlook itself, not by your mail server
Classic Outlook, Microsoft 365	35 MB to send by default, 150 MB at most	Your admin sets the number
New Outlook for Windows, Microsoft 365	35 MB to send by default	Microsoft’s table has no row for it. 35 MB is the mailbox default, and the app may allow less
Outlook on the web, Microsoft 365	25% below the configured limit	112 MB at the 150 MB setting. By the same math, about 26 MB at the default
Outlook for Mac, Microsoft 365	35 MB to send by default, 150 MB at most	New Outlook for Mac also follows the mobile device policy
Outlook for iOS and Android	33 MB per message	20 MB for iCloud. For Microsoft 365, the limits table also lists a 150 MB attachment limit
Exchange Server (your company’s own servers)	10 MB per message by default	Your admin can change it
OneDrive link, Outlook.com or Outlook on the web	2 GB per file	Doesn’t count toward the email size on Outlook.com

Where Microsoft’s Pages Disagree

Outlook.com, 25 MB or 20 MB: Outlook.com’s help says 25 MB. Microsoft’s large-files article says 20 MB for accounts “such as Outlook.com or Gmail.” Stay under 20 MB to be safe.
Work accounts, 35 MB or 10 MB: that article gives 10 MB for Exchange accounts, which matches the Exchange Server default. The limits page, updated October 2026, gives 35 MB for Microsoft 365 mailboxes.
Phones, 33 MB or 150 MB: the limits table lists both. A footnote says the apps use the lowest of three admin settings: MaxAttachmentSize, MaxSendSize and MaxRequestSize. Plan for 33 MB.

Why a File Under the Limit Can Still Fail

The limit is for the whole message. It includes the text and all attachments added together, not each file on its own.
Encoding makes the message larger. Base64 encoding adds about 33%. Microsoft’s example: a 64 MB setting allows a message of about 48 MB. By that math, the default 35 MB may leave room for only about 26 MB of files once mail leaves Microsoft’s datacenters. In Exchange Online, 150 MB holds only inside those datacenters, and mail leaving them tops out at 112 MB. Microsoft doesn’t say how Outlook.com counts this, so leave some margin.
The recipient has a limit too. A message must fit the limits of both sender and recipient, so the other side can refuse a file your account accepts.
Your admin may have set a lower limit. Limits can differ per person, and a mail flow rule can cap any single attachment.

Outlook Attachment Error Messages and What They Mean

“The file you’re attaching is bigger than the server allows. Try putting the file in a shared location and sending a link instead.” Classic Outlook shows this when you add the file. The cause is Outlook’s own 20 MB limit on a POP3, IMAP or HTTP account, or the send limit on your Exchange server.
Bounce code 5.3.4, “Message size exceeds fixed maximum message size”: the message is too large, and either the sending or the receiving system can generate it.
Bounce code 5.2.3, “RESOLVER.RST.RecipSizeLimit; message too large for this recipient”: the message is over that recipient’s limit.

These bounce descriptions come from Microsoft’s Exchange Server reference. To see who refused a message, check the bounce. In Microsoft 365’s newer format, Fix-it owner indicator shows who has to fix it. In the older format, read Generating server and Remote server under Diagnostic information for administrators. If another organization refused it, send a link.

How to Send a Large File in New Outlook

On the Message tab, select Attach File.
For a file already in the cloud, select OneDrive. For a file on your PC, select Browse This PC, pick it, then select the attachment’s down arrow and Upload to OneDrive.
Send it as a link rather than a copy. Microsoft says the link keeps the email small.
Select the arrow beside the attachment to set who can open it.

How to Send a Large File in Classic Outlook

On the Message tab, select Attach File.
For a file already in the cloud, select Browse Web Locations. For a file on your PC, select Browse This PC, pick it, then select the attachment’s down arrow and Upload > OneDrive.
Select the attachment link, then Manage access, to set who can open it.

How to Send a Large File in Outlook on the Web and Outlook.com

Select Attach file > OneDrive, choose the file and select Next.
To limit editing, select More actions on the attachment, then Manage access.

If the file isn’t in OneDrive yet, Outlook.com’s help says to select Attach > Upload and share, then Share link. That page dates from 2023, so your labels may differ.

How to Send a Large File in Outlook for Mac

These steps are from Microsoft’s Mac article.

Select Attach File > OneDrive, choose the file and click Choose. If your account isn’t listed, select Manage Storage Accounts.
For a file on your Mac, select Browse this Mac, then use the arrow next to the file and choose Upload to OneDrive.

How to Send a Large File in the Outlook App (iPhone and Android)

In a new email or a reply, tap the paperclip icon, then Attach file.
Choose where to get the file, then choose the file.
Tap Insert OneDrive for Business Link.

Microsoft’s page gives these steps for iOS and Android and names only OneDrive for Business. With a personal account, start from the paperclip and look for OneDrive as the source.

What the Link’s Permissions Mean

In a work or school account, new and classic Outlook default to Organization can Edit. Check this before you send.

Organization can Edit: anyone in your organization can change the file. In new Outlook they can also share it.
Organization can View: anyone in your organization can read it but not change it.
Recipients can Edit: only the people on your email can change it. In new Outlook they can also share it with others.
Recipients can View: only the people on your email can read it, and they can’t change it.

If a recipient can’t open the file, new Outlook shows the link in red with a warning icon, and Manage access fixes it. Classic Outlook shows a warning under the file and offers Attach as copy, which only helps if the file fits the size limit. On Outlook.com and the web, all recipients can view or edit the same file unless you restrict it.

Zip the File or Shrink Your Pictures

Zipping might shrink a file enough to fit. In Windows, right-click the file and select Show more options > Send to > Compressed (zipped) folder, then attach the zip. In Outlook for Mac, attaching a folder offers Compress, which packages it as one .zip file.

Dragging a picture’s corners changes how large it looks, not its file size. In classic Outlook, attach the pictures, go to File > Info, and under Image Attachments select Resize large images when I send this message. Microsoft says new Outlook can’t reduce an image’s file size.

Blocked File Types Can Look Like the Same Problem

If a small file is refused, check its type. Outlook blocks sending and receiving certain types, such as .exe, .bat and .js, whatever their size. Microsoft recommends a OneDrive or SharePoint link. A .zip also works, because Outlook doesn’t treat that extension as a threat.

What an Admin Can Change

Existing Microsoft 365 mailboxes: Set-Mailbox with -MaxSendSize and -MaxReceiveSize, up to 150 MB. The Exchange admin center shows them under Recipients > Mailboxes, then Manage message size restriction.
New mailboxes: Set-MailboxPlan. It doesn’t change existing ones.
Phones and new Outlook for Mac: these use the lowest of MaxAttachmentSize (mobile device mailbox policy), MaxSendSize and MaxRequestSize, so raising one alone may change nothing.

No admin setting changes another organization’s limit. Personal Outlook.com accounts have no admin, and the Outlook.com pages cited here describe no way to raise the size.

The Classic Outlook Registry Value, and What It Won’t Do

Microsoft documents one registry value, for POP3, IMAP and HTTP accounts only. It changes Outlook’s own 20 MB check. It doesn’t raise your mail server’s limit or the recipient’s, so a larger message can still be refused. On an Exchange account Outlook uses the server’s limit instead. Back up the registry first.

Exit Outlook. In Registry Editor, go to HKEY_CURRENT_USER\Software\Microsoft\Office\16.0\Outlook\Preferences (15.0 for Office 2013), creating the path if needed. Add a DWORD named MaximumAttachmentSize, in KB: decimal 30720 sets 30 MB.

Frequently Asked Questions

What is the Outlook attachment size limit?
For a personal Outlook.com account, 25 MB according to its own help pages, though another Microsoft page says 20 MB. For a Microsoft 365 work or school mailbox, 35 MB to send and 36 MB to receive by default, and an admin can set up to 150 MB. Classic Outlook limits POP3, IMAP and HTTP accounts to 20 MB.

Why does Outlook say my attachment is too large when it is under the limit?
The limit covers the whole message, including text and every attachment. Encoding can add about 33% to mail leaving Microsoft’s datacenters, so by that math a 35 MB limit may leave room for only about 26 MB of files. Your admin may also have set a lower limit, and the recipient’s server may refuse the message.

How do I send a file that is too large for Outlook?
Upload it to OneDrive or SharePoint and send a link instead of a copy. The link keeps the email small. Microsoft lists up to 2 GB per linked file on Outlook.com and the web. You can also zip the file, which may shrink it enough to fit.

Can I increase the attachment size limit in Outlook?
Only partly. In Microsoft 365 an admin can raise your mailbox to 150 MB. In classic Outlook with a POP3, IMAP or HTTP account, the MaximumAttachmentSize registry value changes Outlook’s own check, not the server’s limit. Microsoft’s Outlook.com pages describe no way to raise the limit.

Who can open a file I send as a OneDrive link?
It depends on the link. In a work or school account, new and classic Outlook default to Organization can Edit, so anyone in your organization can change the file. Choose Recipients can View if only the people on your email should read it. New and classic Outlook warn you if a recipient can’t open the file.