I am writing with reference to your enquiry of 6 November.
Opening Reference (very precise)
We are writing with reference to your advertisement ...
According to your brochure,I would like to know further details.Would you please let us have further information about...
We'd appreciate it if you could let us have this information soon because we need to make a
purchase decision by the end of the month.We would appreciate it if you could let us have this information as soon as possible
Please feel free to email me if you have any questions/queries.
This is to inform you that…