I was just browsing through some journals and found some common mistakes we write in every email. You are well aware what we write at the end of email: which is also called Complimentary Close:

Yours sincerely, Yours faithfully, warm regards or best wishes...

If you Know someone or the letter starts with Dear John--- closing should be Yours Sincerely.

If you don't know someone or just addressing Dear Sir/ Madam..., closing should be Yours Faithfully

If someone is your friend or close on..... closing should be Warm Regards...its kind of informal

However people do not bother with these Complimentary closing...but there is no harm in writing Correctly. Try these