Requesting Information
If you need some information from another company, at the start of a letter you may use sentences like :

．We are writing to enquire about…
We are writing to enquire about the price of the Shining Series Shampoo.

．We are writing in connection with…
We are writing in connection with the Ad you posted on the China Times yesterday.

．We are interested in... and we would like to know…
We are interested in your product No.2254, and we would like to know more information about them.

And If you are answering a letter, you can start by using the following phrases :

．Thank you for your letter of (date) ...

asking if…
enquiring about…
enclosing about…
concerning…

Thank you for your letter of March 11 enquiring about the price of the Shining Series Shampoo.

．We have received your letter of (date)

asking if…
enquiring about…
enclosing about…
concerning…

We have received your letter of February 14 concerning our product No.2254.

Referring
To highlight the subject of your letter, you may use :

．With reference to…, ……
With reference to the invoice (No. 254) for the photocopier, we found that….

．Further to…, ……
Further to our meeting on Feb. 26, we think that…

．I am writing in connection with…
I am writing in connection with your application for a post as a teller in our branch.

Informal, Personal business letters
If you are writing a personal letter, or some letters to your close business partners, you may start the letter with some informal sentences :

．It was a pleasure to…
It was a pleasure to meet you in the Taipei Trade Fair yesterday.

．It was good to…
It was good to talk to you on the phone this morning.

．It was a pity that…
It was a pity that I couldn’t come to the meeting on Tuesday.

．I am sorry that…
I am sorry that I missed you when you visited my office last week.