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.