If you have tried to attach large sized files in Outlook 2010 (files greater than 20MB in size), then you might have probably noticed that Outlook 2010 gives a error. Outlook will give you an error when inserting large attachments in your email and will not allow you to add the attachment. This is in order to prevent the message from lying in the Outbox without being sent. For example if your email server allows 30MB attachment sizes, Outlook 2010 will still not allow you to send more than 20MB.