How to Begin & Close an Email

If you know the recipient's name, it is usual to use a personal greeting, e.g.
Dear Mr Ashton
Dear Miss Agnes
Dear Jakie

If your email is addressed generally to an organisation and not to a specific person, the more formal greeting should be used:
Dear Sirs

If your email is addressed to a head of a department or the head of an organisation whose name is not known, it would be more appropriate to use the following greeting:
Dear Sir or Madam

The two common closings are:
Yours faithfully (used only with Dear Sirs/Dear Sir or Madam)
Yours sincerely (used with personal greetings e.g. Dear Mr Ashton)