Specify the nature of the project (in as much detail as is necessary to thoroughly define your needs), time constraints, deadline for responding and to whom the proposal or quote should be directed.
1234, Main Street
Boston, MA 02123
<Recipient Address Goes Here>
Abc Company is requesting <quotation/bid/proposal>s for <nature of project>.
Your <quotation/bid/proposal> should be submitted to <name and address> no later than <deadline>.
encl: <List of enclosed items goes here>