Last reviewed on October 6, 2014   —  34 Comments

Attachment size warningWe’re starting to see reports that begin something like this:

“We’re using a sendmail server. When we use Outlook 2010 and try to send attachments over 20MB we get an error: “The attachment size exceeds the allowable limit”. This works fine under Outlook 2003.”

The default limit is 20 MB (20480kb), which is about right for most ISPs. This limit eliminates the problem with stuck messages: If you try to send a message using SMTP, you get an NDR back into your Inbox telling you the message is too large. Outlook wastes a lot of time uploading the huge file that will never send and this prevents the sending of any other mail.

Exchange server accounts should use the message size set for the user account. Exchange 2010 users will see a mailtip above the To field instead of the warning dialog.

Mailtips warning

If the MaximumAttachmentSize is set higher on the client than the Exchange account is allowed to send, the message will not send. The Send and Receive Progress Dialog will show this error:

Task ‘ – Sending’ reported error (0x80040610) : ‘The message being sent exceeds the message size established for this user.’

If you can send larger attachments you can edit the registry to allow larger limits. While you can set it to 0 for unlimited message size, its better to set the limit to the size your ISP allows.

Registry editor

Open the registry editor and browse to:

Outlook 2013:


Outlook 2010:


Then add a new DWORD value: MaximumAttachmentSize

Unlimited message size uses a value of 0. For a specific message size (recommended) enter the value in Kb. You may want to round the value down to allow for overhead, so 50MB = 50000.

Users are reporting problems using the Send to mail recipient command in Windows Explorer when the default size is set to unlimited.

Error messages include the following:
This error can occur if you attempt to send a Word document as an e-mail attachment in Word and the MAPI session was closed and Word is no longer able to connect to that MAPI session. It can also occur if there is a problem with the fax configuration.
To correct a MAPI related error: restart the MAPI e-mail program (for example, Outlook) or save and close the document, and then restart Word after restarting your MAPI e-mail application. Word will establish a new MAPI session, allowing the document to be sent.”

If your mail server limits you to smaller attachment sizes, you can set the key to prevent an NDR when you attempt to send messages that are too large.

Instant Fix

You can can change the dword value in code below if needed (its set for 30 MB) then copy and paste into notepad and save as “MaximumAttachmentSize.reg”. You’ll double click on the saved file to install it in your registry.

Windows Registry Editor Version 5.00


Download a ready-to-run registry file to set the maximum attachment size to 30 MB attachments

Outlook 2013Outlook 2010

Email Compression Tools

If you use tools such as WinZip’s Companion which compress large attachments automatically after you add them to the email message, you’ll want to set the maximum allowed size at least twice as large as allowed by your email service, or set it to 0 to disable completely. Outlook checks the attachment size as soon as you add the attachments, not before you send the message.


  1. gayle bondy says

    Am 70 years old, so don't expect you are talking to a peer. For the first time in many years, on Outlook 2010 only, my attached PDF files are shrunk. When I click to open, it looks like the doc is about 70% of normal. When I print, it is still about 70% of normal. It says in the tag that the size was reduced for email, but my son guarantees that has nothing to do with printing a form and seeing teensy print and white space for the first 25% of the paper (top). I can't find any "help" for this! Answer if possible pretty please!

    • Diane Poremsky says

      Outlook didn't do it. :)

      What PDF application do you use? I'l see what i can find out - i'd never heard of pdf's getting shrunk for email.

  2. John Welch says

    This is sad. Back when we all used unix there was a "Split" command that would break up a file into small chunks and the email on the other end would re-assemble. We are slipping backwards it seems.

    • Diane Poremsky says

      Outlook no longer includes the ability to split files (since Outlook 2002) because, as mailbox and allowed attachment sizes grew, very few people used it and too many people had no idea how to put the attachment pieces together, generating a lot of help desk calls. Zipping files to reduce size is often better, or use an online file storage system and send a link... or split them outside of Outlook- I think winzip can still split files.

      If you receive a split file, Outlook should be able to put it together.

  3. Les says

    Even though we have a 100mb limit set on our exchange box, I'd like to give the users a pop up warning when they attach 60mb file with a warning like you're in danger of exceeding the maximum file size limit. Please consider splitting your attachments among a few emails rather than just one.Can this be done? We are using exchange 2003 and outlook 2010.Thanks

  4. gary says

    when I set the value to 0 for outlook 2013,right clicking a file and selecting send to mail recipient does not work. the compose window does not open.

  5. Pat Kaley says

    I have a client who sends wma files of recorded meeting minutes. My Outlook will not receive files over 14 MB - however, my home computer will receive the same files with no problem. What's going on?

    • Diane Poremsky says

      Do you have the same account set up on both? Usually the problem is that the email account has a maximize message size set, but depending on your config, a firewall or security software could block large files too.

  6. Mat says

    We have Outlook 2007 SP3 here. As mentioned above, the registry setting does not work for SP3. So what is the workaround then? Thanks

    • Diane Poremsky says

      Are you using POP3/IMAP or Exchange server?

      At this time, there is no work around that I'm aware of but I'm looking into it.

    • Diane Poremsky says

      Is the file size warning coming from the exchange server? It will check file sizes too. Or are you trying to be warned when the file is too large for the server settings?

    • Diane Poremsky says

      Glad I didn't bet - all of the complaints I'm seeing about it not working are for imap. I'm not sure if all are GoDaddy accounts but at least some were. I'll look into it.

  7. Jeremy Patston says

    Hi Diane, I'm using Windows 8 - when I left click a file and select the "Send to mail recipient", I get the little box that asks you to select the file size, but when I do that, I don't get an Outlook mail with the attachment appearing at all (or anything else visible). I've checked the registry folder "Preferences" as per your commentary and I don't have a "MaximumAttachmentSize" dword file either. Will your fix with the dword registry file work, or is mine a different issue?! Thanks, Jeremy

    • Diane Poremsky says

      No, i don't think this is your problem. What version of Outlook are you using?

    • Diane Poremsky says

      You definitely want outlook.exe. You most likely have C2R, so the files are under C:\Program Files\Microsoft Office 15\root\office15\ (or in Program files (x86) if using 32bit Office on 64bit windows.)

  8. Jeremy Patston says

    In C:\Program Files\Microsoft Office 15\root\office15\ there's only an Application file called "Outlook" with the new blue and white Outlook icon (aw, pretty...). It doesn't say .exe in the filename or anywhere else. When I left click on it and go into Properties, there's only 4 tabs: General, Security, Details and Digital Signatures, no Compatibility. "Troubleshoot Compatibility" is in the left click menu, but I can't get through to anything that looks like it is going to allow me to deselect compatibility there...

    • Diane Poremsky says

      Are you showing the file extensions? Look on the View tab of Windows Explorer and click in the File Name Extensions box to show them.

  9. Jeremy Patston says

    Yes, problem is there's no Compatibility tab on right click Properties - General, Security, Details and Digital Signatures is all. Is there an option to switch Compatibility off if I run through the Troubleshoot Compatibility process?

    • Diane Poremsky says

      No, AFAIK, there is no option to disable it. What type of Windows user account are you using? Maybe it's missing on some account types.

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