I am writing to confirm ...
I am writing to apologize for ...
I am writing to enquire about ...
I am writing to you in response to your advertisement for...
I received your address from + and would like ...
I recently wrote to you about ...
In reply to your letter of 8 May, ...
With reference to your letter of 8 June, I ...
With reference to your advertisement in ...
With reference to your phone call today, ...
After having seen your advertisement in ... , I would like ...
After having received your address from ... , I ...
Thank you for your letter of 8 May.
Thank you for your letter regarding ...
Thank you for your letter/e-mail about ...
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