1.  If you begin your email "Dear Sir or Madam" it should end "Yours sincerely....."

Ans: It's true. Besides, other words can be used in the end such as Best Regards.

 2.  Its ok to write your emails in capital letters.

Ans: It's false because using all capital letters looks as if you're shouting.

3.  You should'nt use SMS abbreviations ie How r u.

Ans: It's false because it's unprofessional and informal.

4.  If you are writing to a female who you dont know you should write "Dear Mrs....."

Ans: It's false. You should write "Dear Ms...."  instead.

5.  If you are writing to someone and you want to refer to a prevoius contact you could say "I am writing to enquire about...".

 Ans: It's false because you should cite the content about the previous email. For instance, you should say, "According to the previous email, I would like to inquire about..."

 6.  If you want to give the recipient bad news you could say "I am sorry to inform you......"

Ans: It's false. You should use "I regret to inform you that.." because it sounds softer and more polite.