Last reviewed on May 8, 2014   —  4 Comments

We're seeing complaints that some parts of a message have characters 10 times larger than expected. The problem comes and goes, and doesn't affect all messages.

When I send an email, the recipient receives my message with parts of the message having 120pt font characters. It's not reproducible.

The cause is an antivirus scanner scanning your email. We believe it is due to a change in mso.dll, first installed by KB2289158. As a result, several antivirus scanners are removing the dot in the font size so 10.0pt becomes 100pt and 12.0pt becomes 120pt. Not all messages are affected and within messages, often just a sentence or word is affected.

Even if you uninstall that update, the mso.dll will be install by later cumulative updates. Also note that the problem is usually with the sender’s computer.

To fix this, you need to disable the email scanning feature of your antivirus software. Scanning your email with an antivirus scanner is not necessary, on either inbound to outbound email. Microsoft Outlook does not run active content in email and attachments are automatically saved (to the securetemp folder) before Outlook opens them, so your antivirus will pick up any viruses at that time.

If your antivirus software installs an Outlook add-in, disable or uninstall it. Reports from other users indicate the problem is with the Outlook add-ins. While email scanning is not necessary, using the scanning feature supplied for other email clients does not appear to cause this problem.

Disabling email scanning will not fix messages already in your Inbox, but future messages should not be affected.

To disable the COM Addin:

  • In Microsoft Outlook 2010, go to File, Options, Add-ins. Click on the Go button at the bottom of the screen to open the Addin dialog. Uncheck the antivirus addin to disable the add-in.
  • In Microsoft Outlook 2007 go to Tools, Trust Centers, Add-ins, Go button at the bottom of the screen to disable the antivirus add-in.
  • In Outlook 2003 and older, look in Tools, Options, Other, Advanced, Com add-ins

Do not disable your antivirus completely – only disable the email scanning module!

If this does not solve the problem, disable email scanning in the antivirus software. You may need to uninstall the antivirus software and reinstall using a custom option, choosing not to install the email scanner module.

McAfee, Trend, and AVG are known to cause this problem (and others) but it may not be limited to these three antivirus vendors. Microsoft's Security Essentials does not scan email as it downloads.

Do not disable the antivirus completely – only disable the email scanning module!

Other causes

There are two other causes of large fonts in email. In both cases, the entire message is affected, not just a sentence or two as it is when the anti-virus scanner is the cause.

Zoom: when zoom is the problem, its usually because fonts are tiny, not too large. Hold Ctrl as you scroll the mouse wheel, press Ctrl+ the plus or minus key or use the Zoom menu to change the setting.

Windows Display settings: go to Control panel, Display (use Search if you don't see it). If Windows is configured for settings above 100%, Outlook's dialogs can be hard to read and buttons may be off the screen.


  1. judy says

    Thanks for this idea, but alas, I have Microsoft Security Essentials and there is no antivirus email scanning. So this just keeps happening. Any other ideas on how to solve the supersizing of fonts in middle of some - not all - messages?

    • Diane Poremsky says

      This is for messages you send? Are the messages messed up in the sent folder? It's possible the problem is on the recipients side.

  2. nate says

    Same issue here. two years ago it was an old novell gateway not re encoding a soft line break correctly. If the period fell at the end of the line, it ended up being stripped out and 10.0 became 100

  3. KJ says

    I had Total Defense Internet Security Suite Installed on a pc with newly installed Office 2013. The large font problem in Outlook email that I sent appeared immediately. Specifically, the problem was very large fonts appearing in the first line (and occasionally at spots in my signature) -- 10 times the prescribed font of size of 10. I got MS support and had Office 2013 reinstalled. Problem remained. I had my email service provider refresh my email settings. Problem remained. I closed my email account on my pc and established a new account (same email address). The problem remained. I researched it on line and -- once again -- ended up on the slipstick site. Per the comments on similar issues that I found here, I turned off the email scan portion of Total Defense. The problem remained. I then uninstalled Total Defense and installed Microsoft Security Essentials. The problem disappeared! I am running earlier installs of Total Defense Internet Security Suite on other computers (all Office 2013 or Office 2010) without any problems of this nature. Weird science! In any event, the above steps on the one pc solved a problem that had vexed technical folks at both MS and my email provider.

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