In case I haven’t mentioned this before —

Postage is only valid in the country of origin, so Canadian postage has no value in the United States. If you want to send an SASE internationally, you should include international reply coupons (IRCs), which should be available at any post office.

We get a lot of foreign SASEs with foreign postage (the most frequent offenders are Canadians, thus my using them in the above example). But you Americans out there should also remember this when submitting to foreign markets.