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I'm mailing out several CDs together and am trying to determine the cheapest shipping method. Ideally I would like to use a cardboard mailer (see attached image) but I'm pretty sure that's not allowed. The item weighs 4.1oz and it just slightly thick...

I've read through a handful of threads about this but I'm still a bit confused. If I use a mailer like the one pictured to mail out a CD, what is the cheapest shipping option? I've gathered that it might be First Class Parcel for $2.66? Are there any...