Business letters phrases

I/- Opening lines
With reference to your letter of 8 June, I ...
I am writing to enquire about ...
After having seen your advertisement in ... , I would like ...
After having received your address from ... , I ...
I received your address from ... and would like ...
We/I recently wrote to you about ...
Thank you for your letter of 8 May.
Thank you for your letter regarding ...
Thank you for your letter/e-mail about ...
In reply to your letter of 8 May, ...
II/- Closing lines
If you require any further information, feel free to contact me.
I look forward to your reply.
I look forward to hearing from you.
I look forward to seeing you.
Please advise as necessary.
We look forward to a successful working relationship in the future.
Should you need any further information, please do not hesitate to contact me.
Once again, I apologise for any inconvenience.
We hope that we may continue to rely on your valued custom.
I would appreciate your immediate attention to this matter.
III/- When 'Yours faithfully' and when 'Yours sincerely' in a business letter?
When the recipient's name is unknown to you:
Dear Sir ... Yours faithfully
Dear Madam ... Yours faithfully
Dear Sir or Madam ... Yours faithfully
When you know the recipient's name:
Dear Mr Hanson ... Yours sincerely
Dear Mrs Hanson ... Yours sincerely
Dear Miss Hanson ... Yours sincerely
Dear Ms Hanson ... Yours sincerely
When addressing a good friend or colleague:
Dear Jack ... Best wishes/Best regards
Addressing whole departments:
Dear Sirs ... Yours faithfully