Suggested margins for University letterhead are as follows:
Left Margin: .5"
Date: 2" from the top
Mailing Address: 2.375" from top [if using window envelope, indent 1" from left margin]
Salutation: 3.375" from top
If using window envelopes, it's important to format the document having the address indented 1" from the left side of the paper, and 2.375" from the top of the page. Proper folding is also important. If not done properly the mailing piece will be rejected by the US Postal Service. A "tap test" of the letter will help you see that the address, but no other type, is showing through the window of the envelope. (See Below) Before running a large batch of letters for mailing, be sure to print a sample to test.
Tap Test: A "tap test" is a method used to see if mail meets USPS regulations (DMM 601.6.4). The mail is tapped on the top, bottom, right and left side. The delivery address must remain visible in the window with 1/8" clearance at all times.