Offering assistance
Giving the reason for writing
Giving good news
Giving bad news
Enclosing something
Making reference
Referring to future contact
Making a request
I am pleased to ...
If you require any further information, please do not hesitate to contact us.
I am writing to ...
I look forward to receiving your reply.
We would be grateful if you could ...
With reference to your letter of ...
I am afraid that ...
I enclose ...