well, you have a few ways to go. with that size, there isn't (i think?) an envelope size that fits it closely, although you could make homemade envelopes. you may be able to find a template online somewhere, although you would need pretty large paper in order to cover that size zine. aside from that, you could always just stick it in a large, 8.5 x 10 inch (is that right? or 9x12) envelope and mail that way. a third option: if you've left room on one side of your cover for addresses, you can make it a self-mailer, especially if you've got a cardstock cover (i.e. stick it in the mail as is, without an envelope). see chester's questions about that in this thread.

as to rate and all that, media mail is often the cheapest way to send printed matter if it's heavy. so if you're sending several copies to one place/person, do media mail. otherwise, regular first class is probably the way to go unless the zine is unusually heavy (because media mail costs $1.42 for up to 1 pound - but even my heavy Tenderfoot 2 costs less than $1.42 to mail first class, so it doesn't make sense to go media mail, which often takes longer). you might want to invest in a cheapo postage scale (not the digital kind, they get pricey) or else just take 'em to the post office to weigh. most of the zines i get in the mail seem to run 60 or 83 cents to mail.

i don't know - am i answering your questions here? or just making it sound more confusing? :)

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Tenderfoot: a compilation zine about firsts ~
www.tenderfootzine.com