CRM 2011 has a configurable setting where you can set the “Maximum file size limit for attachments”. This is under the Email tab of the System Settings (see screenshot below).
Although this setting is under the Email tab of System Settings, it limits the size of files for the following –
If you set the Maximum file size to 0, it will restrict you from:
Per this MSDN article (http://msdn.microsoft.com/en-us/library/8c947e83-6765-41d9-b4b7-c078a68257eb), here is a brief description of this setting –
The maximum size of files that can be uploaded is determined by the Organization.MaxUploadFileSize property. This property is set in the E-mail tab of the System Settings in the application. This setting limits the size of files that can be attached to email messages, notes, and Web resources. The default setting is 5MB.