An email message attachment name that contains non-ASCII characters and is longer than 41 UTF-8 encoded bytes is encoded two times before transmission in an application that is compiled for the .NET Framework 4


Symptoms


Consider the following scenario:
  • You run an application that is compiled for the Microsoft .NET Framework 4.
  • The application calls the System.Net.SmtpClient class to send an email message and uses the Attachment class to attach files to a MailMessage object.
  • The attachment name contains non-ASCII characters and is longer than 41 UTF-8 encoded bytes.

In this scenario, the attachment name is unexpectedly encoded two times before transmission. Then, the email message receiver finds a truncated encoded name but not the original name in the attachment.

Cause


This problem occurs because of an issue in the .NET Framework 4. The SMTP encodings were rewritten to include correct folding per RFC standards of line-length limits. This behavior inserts additional carriage return line feed (CRLF) characters when the name string is too long. These additional control characters cause the attachment name to be encoded again.

Resolution


Hotfix information

A supported hotfix is now available from Microsoft. However, it is intended to correct only the problem that is described in this article. Apply it only to systems that are experiencing this specific problem. This hotfix may receive additional testing. Therefore, if you are not severely affected by this problem, we recommend that you wait for the next software update that contains this hotfix.

To resolve this problem immediately, contact Microsoft Customer Support Services to obtain the hotfix. For a complete list of Microsoft Customer Support Services telephone numbers and information about support costs, visit the following Microsoft website:Note In special cases, charges that are ordinarily incurred for support calls may be canceled if a Microsoft Support Professional determines that a specific update will resolve your problem. The usual support costs will apply to additional support questions and issues that do not qualify for the specific update in question.

Note You can download this hotfix rollup from the following Microsoft Connect website:

Prerequisites

You must have the Microsoft .NET Framework 4 installed to apply this hotfix.

Restart information

You do not have to restart the computer after you apply this hotfix.

File information

The English version of this hotfix has the file attributes (or later file attributes) that are listed in the following table. The dates and times for these files are listed in Coordinated Universal Time (UTC). When you view the file information, it is converted to local time. To find the difference between UTC and local time, use the Time Zone tab in the Date and Time item in Control Panel.

For all supported x86-based versions of Windows XP, of Windows Server 2003, of Windows Vista, of Windows Server 2008, of Windows 7, and of Windows Server 2008 R2
File nameFile versionFile sizeDateTimePlatform
SetupUi.dll10.0.30319.364295,24828-Sep-201005:19x86
Setupengine.dll10.0.30319.364809,30428-Sep-201005:19x86
Setup.exe10.0.30319.36478,15228-Sep-201005:19x86
System.dll4.0.30319.3643,482,44028-Sep-201011:15x86
For all supported x64-based versions of Windows XP, of Windows Server 2003, of Windows Vista, of Windows Server 2008, of Windows 7, and of Windows Server 2008 R2
File nameFile versionFile sizeDateTimePlatform
SetupUi.dll10.0.30319.364295,24828-Sep-201005:19x86
Setupengine.dll10.0.30319.364809,30428-Sep-201005:19x86
Setup.exe10.0.30319.36478,15228-Sep-201005:19x86
System.dll4.0.30319.3643,482,44028-Sep-201011:15x86
For all supported IA-64-based versions of Windows XP, of Windows Server 2003, of Windows Vista, of Windows Server 2008, of Windows 7, and of Windows Server 2008 R2
File nameFile versionFile sizeDateTimePlatform
SetupUi.dll10.0.30319.364295,24828-Sep-201005:19x86
Setupengine.dll10.0.30319.364809,30428-Sep-201005:19x86
Setup.exe10.0.30319.36478,15228-Sep-201005:19x86
System.dll4.0.30319.3643,482,44028-Sep-201011:15x86


Status


Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.

More Information


For more information about RFC standards and about CRLF characters, visit the following Microsoft Developer Network (MSDN) website: