Wonder your mail contains Sensitive or Confidential materials or Phonographic which you intend to send one of your friend but unfortunately you misspell the email address and it was sent to someone whom you don’t know! Just think about the sequences or how bad the user might have felt or hurt reading your mail but mistakes or mistakes. What if the user takes a legal action against you ? So although its recommended to be safe while sending email, i strongly recommend you to add email disclaimers for your outgoing emails.

What is Disclaimer ?
It is a statement that states that entity is not responsible for something in some manner. There are many types of Disclaimers. E-mail Disclaimers alerts the readers to risks involved. These disclaimers are appended to email either as signature or attachment. I cannot assure you that email disclaimers will protect against actual libelous but it will certainly help you in some situations from liability.

Example of a standard email disclaimer which i use

This email and any files transmitted with it are confidential and intended solely for the use of the individual or entity to whom they are addressed. If you have received this email in error please notify the system manager. Please note that any views or opinions presented in this email are solely those of the author and do not necessarily represent those of the company. Finally, the recipient should check this email and any attachments for the presence of viruses. Sankar Anand or Gmail™ of Google® accepts no liability for any damage caused by any virus transmitted by this email.

Adding Disclaimers as Signature in your mail:
Gmail or Googlemail:
*Click Settings.
*Enter your new signature text in the box at the bottom of the page next to the Signature option. As you type, the radio button will shift from No Signature to the text box.
*Click Save Changes.

Yahoo Mail :
* Select Mail Options from the Yahoo! Mail navigation bar
* Follow the Signature link (under Personalization).
* Enter the desired signature in the text field.
* Click Save.
Other Mail Service users can contact their local mail providers for instruction on adding signature to their outgoing mails.

You can get more samples of email disclaimers here.