Wait to Decline?

[morningcrafter]

I received an email from the head of a graduate English program offering me full tuition waiver, sizable stipend and a one time books stipend. Their offer is far better than my others, so I want to decline them quickly in order to open up spots for other applicants, but I still haven't received my official packet from the school with the great offer. The email was an informal and personal back and forth type thing and not from the graduate school, but just the English dept.'s graduate director.

Should I decline my other offers (one funded, two unfunded) or should I wait until I get the official acceptance in the mail (which could take two weeks given my small town's postal reputation)?

[wtncffts]

I received an email from the head of a graduate English program offering me full tuition waiver, sizable stipend and a one time books stipend. Their offer is far better than my others, so I want to decline them quickly in order to open up spots for other applicants, but I still haven't received my official packet from the school with the great offer. The email was an informal and personal back and forth type thing and not from the graduate school, but just the English dept.'s graduate director.

Should I decline my other offers (one funded, two unfunded) or should I wait until I get the official acceptance in the mail (which could take two weeks given my small town's postal reputation)?

I would decline two of the other offers and keep one (I'm guessing the funded one) just in case.