a place for zinesters - writers and readers
I decided to test this out, so I mailed myself a clasp-closed small envelope. It got to me fine with the 'letter rate' postage on it -- no nonmachinable surcharge, no postage due. Since clasps are supposed to make an envelope considered nonmachinable (and therefore subject to the surcharge), I guess this is another case of mail rules being unequally applied.
Whenever I bring something up to the counter with a metal clasp, the clerks always charge me the "large envelope" rate. Being the tightwad that I am, I pull off the metal clasps from all envelopes before I mail them. Envelopes without metal clasps seem harder to find around here.