You cannot change the font size in Windows Live Mail or in Windows Mail after you install Internet Explorer 9
From Microsoft. This might help.
Symptoms
When you try to change the font size that is used for reading messages in Windows Live Mail or in Windows Mail, the font size does not change. For example, consider the following scenario:
You have Windows Live Mail 2011 installed, and you have set up access to an email account to view your messages in the Inbox.
You install Windows Internet Explorer 9.
You start Windows Live Mail. Your Inbox contains HTML email messages.
You try to change the font size so that the messages that are displayed can be read more easily. To do this, follow these steps:
On the Windows Live Mail tab, click Options and then click Mail.
On the Read tab, click Fonts.
In the Font size box, select Smallest, and then click OK.
Click OK to close the Options dialog box.
In this scenario, the font size is not changed.
Resolution
To resolve this problem, install this update.
Security update information
To resolve this issue, install the most recent cumulative security update for Internet Explorer. To do this, visit the following Microsoft website:
http://update.microsoft.comFor more technical information about the most recent cumulative security update for Internet Explorer, visit the following Microsoft website:
Microsoft Learn: Build skills that open doors in your career This update was first included in security update 2586448.
For more information, click the following article number to view the article in the Microsoft Knowledge Base:
2586448 MS11-081: Cumulative Security Update for Internet Explorer: October 11, 2011
Status
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.